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Hilscher MM, Mikulovic S, Perry S, Lundberg S, Kullander K. The alpha2 nicotinic acetylcholine receptor, a subunit with unique and selective expression in inhibitory interneurons associated with principal cells. Pharmacol Res 2023; 196:106895. [PMID: 37652281 DOI: 10.1016/j.phrs.2023.106895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 08/21/2023] [Accepted: 08/23/2023] [Indexed: 09/02/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) play crucial roles in various human disorders, with the α7, α4, α6, and α3-containing nAChR subtypes extensively studied in relation to conditions such as Alzheimer's disease, Parkinson's disease, nicotine dependence, mood disorders, and stress disorders. In contrast, the α2-nAChR subunit has received less attention due to its more restricted expression and the scarcity of specific agonists and antagonists for studying its function. Nevertheless, recent research has shed light on the unique expression pattern of the Chrna2 gene, which encodes the α2-nAChR subunit, and its involvement in distinct populations of inhibitory interneurons. This review highlights the structure, pharmacology, localization, function, and disease associations of α2-containing nAChRs and points to the unique expression pattern of the Chrna2 gene and its role in different inhibitory interneuron populations. These populations, including the oriens lacunosum moleculare (OLM) cells in the hippocampus, Martinotti cells in the neocortex, and Renshaw cells in the spinal cord, share common features and contribute to recurrent inhibitory microcircuits. Thus, the α2-nAChR subunit's unique expression pattern in specific interneuron populations and its role in recurrent inhibitory microcircuits highlight its importance in various physiological processes. Further research is necessary to uncover the comprehensive functionality of α2-containing nAChRs, delineate their specific contributions to neuronal circuits, and investigate their potential as therapeutic targets for related disorders.
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Affiliation(s)
- Markus M Hilscher
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden; Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Sanja Mikulovic
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden; Leibniz Institute for Neurobiology, Cognition & Emotion Laboratory, Magdeburg, Germany; German Center for Mental Health(DZPG), Germany
| | - Sharn Perry
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden; Wicking Dementia Research and Education Centre, University of Tasmania, Hobart, Australia
| | - Stina Lundberg
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden
| | - Klas Kullander
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden.
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York JM, Borghese CM, George AA, Cannatella DC, Zakon HH. A potential cost of evolving epibatidine resistance in poison frogs. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.04.522789. [PMID: 36711899 PMCID: PMC9882002 DOI: 10.1101/2023.01.04.522789] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Background Some poison arrow frogs sequester the toxin epibatidine as a defense against predators. We previously identified a single amino acid substitution (S108C) at a highly conserved site in a neuronal nicotinic acetylcholine receptor (nAChR) ß2 subunit that prevents epibatidine from binding to this receptor. When placed in a homologous mammalian nAChR this substitution minimized epibatidine binding but also perturbed acetylcholine binding, a clear cost. However, in the nAChRs of poison arrow frogs, this substitution appeared to have no detrimental effect on acetylcholine binding and, thus, appeared cost-free. Results The introduction of S108C into the α4β2 nAChRs of non-dendrobatid frogs also does not affect ACh sensitivity, when these receptors are expressed in Xenopus laevis oocytes. However, α4β2 nAChRs with C108 had a decreased magnitude of neurotransmitter-induced currents in all species tested ( Epipedobates anthonyi , non-dendrobatid frogs, as well as human), compared with α4β2 nAChRs with the conserved S108. Immunolabeling of frog or human α4β2 nAChRs in the plasma membrane using radiolabeled antibody against the β2 nAChR subunit shows that C108 significantly decreased the number of cell-surface α4β2 nAChRs, compared with S108. Conclusions While S108C protects these species against sequestered epibatidine, it incurs a potential physiological cost of disrupted α4β2 nAChR function. These results may explain the high conservation of a serine at this site in vertebrates, as well as provide an example of a tradeoff between beneficial and deleterious effects of an evolutionary change. They also provide important clues for future work on assembly and trafficking of this important neurotransmitter receptor.
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Mazzaferro S, Strikwerda JR, Sine SM. Stoichiometry-selective modulation of α4β2 nicotinic ACh receptors by divalent cations. Br J Pharmacol 2022; 179:1353-1370. [PMID: 34768309 DOI: 10.1111/bph.15723] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 10/11/2021] [Accepted: 10/18/2021] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND AND PURPOSE α4β2 nicotinic ACh receptors (nAChRs) comprise the most abundant class of nAChRs in the nervous system. They assemble in two stoichiometric forms, each exhibiting distinct functional and pharmacological signatures. However, whether one or both forms are modulated by calcium or magnesium has not been established. EXPERIMENTAL APPROACH To assess the functional consequences of calcium and magnesium, each stoichiometric form was expressed in clonal mammalian fibroblasts and single-channel currents were recorded in the presence of a range of ACh concentrations. KEY RESULTS In the absence of divalent cations, each stoichiometric form exhibits high unitary conductance and simple gating kinetics composed of solitary channel openings or short bursts of openings. However, in the presence of calcium and magnesium, the conductance and gating kinetics change in a stoichiometry-dependent manner. Calcium and magnesium reduce the conductance of both stoichiometric forms, with each cation producing an equivalent reduction, but the reduction is greater for the (α4)2 (β2)3 form. Moreover, divalent cations promote efficient channel opening of the (α4)3 (β2)2 stoichiometry, while minimally affecting the (α4)2 (β2)3 stoichiometry. For the (α4)3 (β2)2 stoichiometry, at high but not low ACh concentrations, calcium in synergy with magnesium promote clustering of channel openings into episodes of many openings in quick succession. CONCLUSION AND IMPLICATIONS Modulation of the α4β2 nAChR by divalent cations depends on the ACh concentration, the type of cation and the subunit stoichiometry. The functional consequences of modulation are expected to depend on the regional distributions of the stoichiometric forms and synaptic versus extrasynaptic locations of the receptors.
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Affiliation(s)
- Simone Mazzaferro
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
| | - John R Strikwerda
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
| | - Steven M Sine
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.,Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.,Department of Neurology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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Hollenhorst MI, Krasteva-Christ G. Nicotinic Acetylcholine Receptors in the Respiratory Tract. Molecules 2021; 26:6097. [PMID: 34684676 PMCID: PMC8539672 DOI: 10.3390/molecules26206097] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/01/2021] [Accepted: 10/06/2021] [Indexed: 02/07/2023] Open
Abstract
Nicotinic acetylcholine receptors (nAChR) are widely distributed in neuronal and non-neuronal tissues, where they play diverse physiological roles. In this review, we highlight the recent findings regarding the role of nAChR in the respiratory tract with a special focus on the involvement of nAChR in the regulation of multiple processes in health and disease. We discuss the role of nAChR in mucociliary clearance, inflammation, and infection and in airway diseases such as asthma, chronic obstructive pulmonary disease, and cancer. The subtype diversity of nAChR enables differential regulation, making them a suitable pharmaceutical target in many diseases. The stimulation of the α3β4 nAChR could be beneficial in diseases accompanied by impaired mucociliary clearance, and the anti-inflammatory effect due to an α7 nAChR stimulation could alleviate symptoms in diseases with chronic inflammation such as chronic obstructive pulmonary disease and asthma, while the inhibition of the α5 nAChR could potentially be applied in non-small cell lung cancer treatment. However, while clinical studies targeting nAChR in the airways are still lacking, we suggest that more detailed research into this topic and possible pharmaceutical applications could represent a valuable tool to alleviate the symptoms of diverse airway diseases.
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Rivera-Perez LM, Kwapiszewski JT, Roberts MT. α 3β 4 ∗ Nicotinic Acetylcholine Receptors Strongly Modulate the Excitability of VIP Neurons in the Mouse Inferior Colliculus. Front Neural Circuits 2021; 15:709387. [PMID: 34434092 PMCID: PMC8381226 DOI: 10.3389/fncir.2021.709387] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 07/19/2021] [Indexed: 12/03/2022] Open
Abstract
The inferior colliculus (IC), the midbrain hub of the central auditory system, receives extensive cholinergic input from the pontomesencephalic tegmentum. Activation of nicotinic acetylcholine receptors (nAChRs) in the IC can alter acoustic processing and enhance auditory task performance. However, how nAChRs affect the excitability of specific classes of IC neurons remains unknown. Recently, we identified vasoactive intestinal peptide (VIP) neurons as a distinct class of glutamatergic principal neurons in the IC. Here, in experiments using male and female mice, we show that cholinergic terminals are routinely located adjacent to the somas and dendrites of VIP neurons. Using whole-cell electrophysiology in brain slices, we found that acetylcholine drives surprisingly strong and long-lasting excitation and inward currents in VIP neurons. This excitation was unaffected by the muscarinic receptor antagonist atropine. Application of nAChR antagonists revealed that acetylcholine excites VIP neurons mainly via activation of α3β4∗ nAChRs, a nAChR subtype that is rare in the brain. Furthermore, we show that acetylcholine excites VIP neurons directly and does not require intermediate activation of presynaptic inputs that might express nAChRs. Lastly, we found that low frequency trains of acetylcholine puffs elicited temporal summation in VIP neurons, suggesting that in vivo-like patterns of cholinergic input can reshape activity for prolonged periods. These results reveal the first cellular mechanisms of nAChR regulation in the IC, identify a functional role for α3β4∗ nAChRs in the auditory system, and suggest that cholinergic input can potently influence auditory processing by increasing excitability in VIP neurons and their postsynaptic targets.
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Affiliation(s)
- Luis M Rivera-Perez
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, Ann Arbor, MI, United States
| | - Julia T Kwapiszewski
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, Ann Arbor, MI, United States
| | - Michael T Roberts
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, Ann Arbor, MI, United States
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Mazzaferro S, Whiteman ST, Alcaino C, Beyder A, Sine SM. NACHO and 14-3-3 promote expression of distinct subunit stoichiometries of the α4β2 acetylcholine receptor. Cell Mol Life Sci 2021; 78:1565-1575. [PMID: 32676916 PMCID: PMC7854996 DOI: 10.1007/s00018-020-03592-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 06/19/2020] [Accepted: 07/01/2020] [Indexed: 02/07/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) belong to the superfamily of pentameric ligand-gated ion channels, and in neuronal tissues, are assembled from various types of α- and β-subunits. Furthermore, the subunits α4 and β2 assemble in two predominant stoichiometric forms, (α4)2(β2)3 and (α4)3(β2)2, forming receptors with dramatically different sensitivity to agonists and allosteric modulators. However, mechanisms by which the two stoichiometric forms are regulated are not known. Here, using heterologous expression in mammalian cells, single-channel patch-clamp electrophysiology, and calcium imaging, we show that the ER-resident protein NACHO selectively promotes the expression of the (α4)2(β2)3 stoichiometry, whereas the cytosolic molecular chaperone 14-3-3η selectively promotes the expression of the (α4)3(β2)2 stoichiometry. Thus, NACHO and 14-3-3η are potential physiological regulators of subunit stoichiometry, and are potential drug targets for re-balancing the stoichiometry in pathological conditions involving α4β2 nAChRs such as nicotine dependence and epilepsy.
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Affiliation(s)
- Simone Mazzaferro
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
| | - Sara T Whiteman
- Enteric Neuroscience Program (ENSP), Division of Gastroenterology & Hepatology, Department of Medicine, Mayo Clinic, Rochester, MN, 55905, USA.
| | - Constanza Alcaino
- Enteric Neuroscience Program (ENSP), Division of Gastroenterology & Hepatology, Department of Medicine, Mayo Clinic, Rochester, MN, 55905, USA
| | - Arthur Beyder
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
- Enteric Neuroscience Program (ENSP), Division of Gastroenterology & Hepatology, Department of Medicine, Mayo Clinic, Rochester, MN, 55905, USA
| | - Steven M Sine
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
- Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
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Mille T, Quilgars C, Cazalets J, Bertrand SS. Acetylcholine and spinal locomotor networks: The insider. Physiol Rep 2021; 9:e14736. [PMID: 33527727 PMCID: PMC7851432 DOI: 10.14814/phy2.14736] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2020] [Revised: 01/05/2021] [Accepted: 01/07/2021] [Indexed: 01/07/2023] Open
Abstract
This article aims to review studies that have investigated the role of neurons that use the transmitter acetylcholine (ACh) in controlling the operation of locomotor neural networks within the spinal cord. This cholinergic system has the particularity of being completely intraspinal. We describe the different effects exerted by spinal cholinergic neurons on locomotor circuitry by the pharmacological activation or blockade of this propriospinal system, as well as describing its different cellular and subcellular targets. Through the activation of one ionotropic receptor, the nicotinic receptor, and five metabotropic receptors, the M1 to M5 muscarinic receptors, the cholinergic system exerts a powerful control both on synaptic transmission and locomotor network neuron excitability. Although tremendous advances have been made in our understanding of the spinal cholinergic system's involvement in the physiology and pathophysiology of locomotor networks, gaps still remain, including the precise role of the different subtypes of cholinergic neurons as well as their pre- and postsynaptic partners. Improving our knowledge of the propriospinal cholinergic system is of major relevance to finding new cellular targets and therapeutics in countering the debilitating effects of neurodegenerative diseases and restoring motor functions after spinal cord injury.
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Affiliation(s)
- Théo Mille
- Université de BordeauxCNRS UMR 5287INCIABordeauxFrance
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Interactions of the α3β2 Nicotinic Acetylcholine Receptor Interfaces with α-Conotoxin LsIA and its Carboxylated C-terminus Analogue: Molecular Dynamics Simulations. Mar Drugs 2020; 18:md18070349. [PMID: 32635340 PMCID: PMC7401271 DOI: 10.3390/md18070349] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Revised: 06/27/2020] [Accepted: 06/30/2020] [Indexed: 12/22/2022] Open
Abstract
Notably, α-conotoxins with carboxy-terminal (C-terminal) amidation are inhibitors of the pentameric nicotinic acetylcholine receptors (nAChRs), which are therapeutic targets for neurological diseases and disorders. The (α3)2(β2)3 nAChR subunit arrangement comprises a pair of α3(+)β2(−) and β2(+)α3(−) interfaces, and a β2(+)β2(−) interface. The β2(+)β2(−) interface has been suggested to have higher agonist affinity relative to the α3(+)β2(−) and β2(+)α3(−) interfaces. Nevertheless, the interactions formed by these subunit interfaces with α-conotoxins are not well understood. Therefore, in order to address this, we modelled the interactions between α-conotoxin LsIA and the α3β2 subtype. The results suggest that the C-terminal carboxylation of LsIA predominantly influenced the enhanced contacts of the conotoxin via residues P7, P14 and C17 on LsIA at the α3(+)β2(−) and β2(+)α3(−) interfaces. However, this enhancement is subtle at the β2(+)β2(−) site, which can compensate the augmented interactions by LsIA at α3(+)β2(−) and β2(+)α3(−) binding sites. Therefore, the divergent interactions at the individual binding interface may account for the minor changes in binding affinity to α3β2 subtype by C-terminal carboxylation of LsIA versus its wild type, as shown in previous experimental results. Overall, these findings may facilitate the development of new drug leads or subtype-selective probes.
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Bertrand D, Wallace TL. A Review of the Cholinergic System and Therapeutic Approaches to Treat Brain Disorders. Curr Top Behav Neurosci 2020; 45:1-28. [PMID: 32451956 DOI: 10.1007/7854_2020_141] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Since its identification over a hundred years ago, the neurotransmitter acetylcholine (ACh) has proven to play an essential role in supporting many diverse functions. Some well-characterized functions include: chemical transmission at the neuromuscular junction; autonomic function in the peripheral nervous system; and, sustained attention, sleep/wake regulation, and learning and memory within the central nervous system. Within the brain, major cholinergic projection pathways from the basal forebrain and the brainstem support these centrally mediated processes, and dysregulation of the cholinergic system is implicated in cognitive decline associated with aging and dementias including Alzheimer's disease. ACh exerts its effects by binding to two different membrane-bound receptor classes: (1) G‑protein coupled muscarinic acetylcholine receptors (mAChRs), and (2) ligand-gated nicotinic acetylcholine receptors (nAChRs). These receptor systems are described in detail within this chapter along with discussion on the successes and failures of synthetic ligands designed to selectively target receptor subtypes for treating brain disorders. New molecular approaches and advances in our understanding of the target biology combined with opportunities to re-purpose existing cholinergic drugs for new indications continue to highlight the exciting opportunities for modulating this system for therapeutic purposes.
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