1
|
Sampat GH, Hiremath K, Dodakallanavar J, Patil VS, Harish DR, Biradar P, Mahadevamurthy RK, Barvaliya M, Roy S. Unraveling snake venom phospholipase A 2: an overview of its structure, pharmacology, and inhibitors. Pharmacol Rep 2023; 75:1454-1473. [PMID: 37926795 DOI: 10.1007/s43440-023-00543-8] [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: 06/12/2023] [Revised: 10/05/2023] [Accepted: 10/06/2023] [Indexed: 11/07/2023]
Abstract
Snake bite is a neglected disease that affects millions of people worldwide. WHO reported approximately 5 million people are bitten by various species of snakes each year, resulting in nearly 1 million deaths and an additional three times cases of permanent disability. Snakes utilize the venom mainly for immobilization and digestion of their prey. Snake venom is a composition of proteins and enzymes which is responsible for its diverse pharmacological action. Snake venom phospholipase A2 (SvPLA2) is an enzyme that is present in every snake species in different quantities and is known to produce remarkable functional diversity and pharmacological action like inflammation, necrosis, myonecrosis, hemorrhage, etc. Arachidonic acid, a precursor to eicosanoids, such as prostaglandins and leukotrienes, is released when SvPLA2 catalyzes the hydrolysis of the sn-2 positions of membrane glycerophospholipids, which is responsible for its actions. Polyvalent antivenom produced from horses or lambs is the standard treatment for snake envenomation, although it has many drawbacks. Traditional medical practitioners treat snake bites using plants and other remedies as a sustainable alternative. More than 500 plant species from more than 100 families reported having venom-neutralizing abilities. Plant-derived secondary metabolites have the ability to reduce the venom's adverse consequences. Numerous studies have documented the ability of plant chemicals to inhibit the enzymes found in snake venom. Research in recent years has shown that various small molecules, such as varespladib and methyl varespladib, effectively inhibit the PLA2 toxin. In the present article, we have overviewed the knowledge of snake venom phospholipase A2, its classification, and the mechanism involved in the pathophysiology of cytotoxicity, myonecrosis, anticoagulation, and inflammation clinical application and inhibitors of SvPLA2, along with the list of studies carried out to evaluate the potency of small molecules like varespladib and secondary metabolites from the traditional medicine for their anti-PLA2 effect.
Collapse
Affiliation(s)
- Ganesh H Sampat
- ICMR-National Institute of Traditional Medicine, Belagavi, Karnataka, 590010, India
- KLE College of Pharmacy, Belagavi, KLE Academy of Higher Education and Research, Belagavi, Karnataka, 590010, India
| | - Kashinath Hiremath
- ICMR-National Institute of Traditional Medicine, Belagavi, Karnataka, 590010, India
- KLE College of Pharmacy, Belagavi, KLE Academy of Higher Education and Research, Belagavi, Karnataka, 590010, India
| | - Jagadeesh Dodakallanavar
- ICMR-National Institute of Traditional Medicine, Belagavi, Karnataka, 590010, India
- KLE College of Pharmacy, Belagavi, KLE Academy of Higher Education and Research, Belagavi, Karnataka, 590010, India
| | - Vishal S Patil
- ICMR-National Institute of Traditional Medicine, Belagavi, Karnataka, 590010, India
- KLE College of Pharmacy, Belagavi, KLE Academy of Higher Education and Research, Belagavi, Karnataka, 590010, India
| | - Darasaguppe R Harish
- ICMR-National Institute of Traditional Medicine, Belagavi, Karnataka, 590010, India.
| | - Prakash Biradar
- KLE College of Pharmacy, Belagavi, KLE Academy of Higher Education and Research, Belagavi, Karnataka, 590010, India.
| | | | - Manish Barvaliya
- ICMR-National Institute of Traditional Medicine, Belagavi, Karnataka, 590010, India
| | - Subarna Roy
- ICMR-National Institute of Traditional Medicine, Belagavi, Karnataka, 590010, India
| |
Collapse
|
2
|
Acharya S, Kundu D, Kim KM. β-Arrestin1 and GPCR kinase2 play permissive roles in Src-mediated endocytosis of α4β2 nicotinic ACh receptors. Br J Pharmacol 2021; 178:3498-3516. [PMID: 33844281 DOI: 10.1111/bph.15495] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 04/02/2021] [Accepted: 04/06/2021] [Indexed: 01/20/2023] Open
Abstract
BACKGROUND AND PURPOSE The α4β2 nicotinic ACh receptor (nAChR), a subtype of the ligand-gated ion channel, is abundantly expressed in the brain and is implicated in several neurological disorders. The endocytosis of nAChRs plays important roles in the pathogenesis of neurological diseases, but the underlying molecular mechanisms remain poorly understood. EXPERIMENTAL APPROACH Loss-of-function approaches and mutants of α4β2 nAChRs that display different endocytic properties were used to identify the cellular components and processes responsible for endocytosis. The signalling cascade that leads to endocytosis was deduced via protein interactions in predicted cellular components. The endocytosis of α4β2 nAChRs was determined and crosschecked using an ELISA and radioligand assay. KEY RESULTS Endocytosis of α4β2 nAChRs occurred through clathrin-mediated endocytosis in a dynamin-dependent manner. 14-3-3η-dependent Src-mediated phosphorylation of the nAChR α4 subunit at Y575 was required for nAChR endocytosis, and this occurred with the assistance of β-arrestin1 and GPCR kinase 2 (GRK2) without the need for kinase activity. Endocytosis triggered the mouse double minute 2 homologue-mediated ubiquitination and subsequent down-regulation of α4β2 nAChRs. CONCLUSIONS AND IMPLICATIONS α4β2 nAChR, an ionophore receptor, employs the metabotropic signalling pathway required for endocytosis, which leads to ubiquitination and down-regulation. Further, GRK2 and β-arrestin1, usually associated with GPCR signalling, are involved in the endocytosis of α4β2 nAChRs via different mechanisms. Considering the functional and pathological implications of nAChR endocytosis, results obtained in this study are crucial for the progression of basic research and clinical investigations.
Collapse
Affiliation(s)
- Srijan Acharya
- Department of Pharmacology, College of Pharmacy, Chonnam National University, Gwangju, Republic of Korea.,Mitchell Cancer Institute, Department of Pathology, College of Medicine, University of South Alabama, Mobile, Alabama, USA
| | - Dooti Kundu
- Department of Pharmacology, College of Pharmacy, Chonnam National University, Gwangju, Republic of Korea
| | - Kyeong-Man Kim
- Department of Pharmacology, College of Pharmacy, Chonnam National University, Gwangju, Republic of Korea
| |
Collapse
|
3
|
Chen J, Loukola A, Gillespie NA, Peterson R, Jia P, Riley B, Maes H, Dick DM, Kendler KS, Damaj MI, Miles MF, Zhao Z, Li MD, Vink JM, Minica CC, Willemsen G, Boomsma DI, Qaiser B, Madden PAF, Korhonen T, Jousilahti P, Hällfors J, Gelernter J, Kranzler HR, Sherva R, Farrer L, Maher B, Vanyukov M, Taylor M, Ware JJ, Munafò MR, Lutz SM, Hokanson JE, Gu F, Landi MT, Caporaso NE, Hancock DB, Gaddis NC, Baker TB, Bierut LJ, Johnson EO, Chenoweth M, Lerman C, Tyndale R, Kaprio J, Chen X. Genome-Wide Meta-Analyses of FTND and TTFC Phenotypes. Nicotine Tob Res 2020; 22:900-909. [PMID: 31294817 DOI: 10.1093/ntr/ntz099] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Accepted: 09/14/2018] [Indexed: 12/19/2022]
Abstract
INTRODUCTION FTND (Fagerstrӧm test for nicotine dependence) and TTFC (time to smoke first cigarette in the morning) are common measures of nicotine dependence (ND). However, genome-wide meta-analysis for these phenotypes has not been reported. METHODS Genome-wide meta-analyses for FTND (N = 19,431) and TTFC (N = 18,567) phenotypes were conducted for adult smokers of European ancestry from 14 independent cohorts. RESULTS We found that SORBS2 on 4q35 (p = 4.05 × 10-8), BG182718 on 11q22 (p = 1.02 × 10-8), and AA333164 on 14q21 (p = 4.11 × 10-9) were associated with TTFC phenotype. We attempted replication of leading candidates with independent samples (FTND, N = 7010 and TTFC, N = 10 061), however, due to limited power of the replication samples, the replication of these new loci did not reach significance. In gene-based analyses, COPB2 was found associated with FTND phenotype, and TFCP2L1, RELN, and INO80C were associated with TTFC phenotype. In pathway and network analyses, we found that the interconnected interactions among the endocytosis, regulation of actin cytoskeleton, axon guidance, MAPK signaling, and chemokine signaling pathways were involved in ND. CONCLUSIONS Our analyses identified several promising candidates for both FTND and TTFC phenotypes, and further verification of these candidates was necessary. Candidates supported by both FTND and TTFC (CHRNA4, THSD7B, RBFOX1, and ZNF804A) were associated with addiction to alcohol, cocaine, and heroin, and were associated with autism and schizophrenia. We also identified novel pathways involved in cigarette smoking. The pathway interactions highlighted the importance of receptor recycling and internalization in ND. IMPLICATIONS Understanding the genetic architecture of cigarette smoking and ND is critical to develop effective prevention and treatment. Our study identified novel candidates and biological pathways involved in FTND and TTFC phenotypes, and this will facilitate further investigation of these candidates and pathways.
Collapse
Affiliation(s)
- Jingchun Chen
- Nevada Institute of Personalized Medicine, University of Nevada Las Vegas, Las Vegas, NV
| | - Anu Loukola
- Department of Public Health, University of Helsinki, Helsinki, FI, Finland.,Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland
| | - Nathan A Gillespie
- Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA
| | - Roseann Peterson
- Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA
| | - Peilin Jia
- School of Biomedical Informatics, University of Texas Health Science Center at Houston, Houston, TX
| | - Brien Riley
- Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA
| | - Hermine Maes
- Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA
| | - Daniella M Dick
- Department of Psychology, Virginia Commonwealth University, Richmond, VA
| | - Kenneth S Kendler
- Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA
| | - M Imad Damaj
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA
| | - Michael F Miles
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA
| | - Zhongming Zhao
- School of Biomedical Informatics, University of Texas Health Science Center at Houston, Houston, TX
| | - Ming D Li
- State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Jacqueline M Vink
- Netherlands Twin Register, Department of Biological Psychology, VU University, the Netherlands.,Behavioural Science Institute, Radboud University, Nijmegen, the Netherlands
| | - Camelia C Minica
- Netherlands Twin Register, Department of Biological Psychology, VU University, the Netherlands.,Neuroscience Campus Amsterdam, the Netherlands.,EMGO+ Institute for Health and Care Research, VU Medical Center, Amsterdam, the Netherlands
| | - Gonneke Willemsen
- Netherlands Twin Register, Department of Biological Psychology, VU University, the Netherlands.,Neuroscience Campus Amsterdam, the Netherlands.,EMGO+ Institute for Health and Care Research, VU Medical Center, Amsterdam, the Netherlands
| | - Dorret I Boomsma
- Netherlands Twin Register, Department of Biological Psychology, VU University, the Netherlands.,Neuroscience Campus Amsterdam, the Netherlands.,EMGO+ Institute for Health and Care Research, VU Medical Center, Amsterdam, the Netherlands
| | - Beenish Qaiser
- Department of Public Health, University of Helsinki, Helsinki, FI, Finland.,Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland
| | | | - Tellervo Korhonen
- Department of Public Health, University of Helsinki, Helsinki, FI, Finland.,Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Finland
| | | | - Jenni Hällfors
- Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland
| | - Joel Gelernter
- Department of Psychiatry, Yale University, New Haven, CT
| | - Henry R Kranzler
- Department of Psychiatry, University of Pennsylvania, Philadelphia, PA
| | - Richard Sherva
- Section of Biomedical Genetics, Department of Medicine, Boston University School of Medicine, Boston, MA
| | - Lindsay Farrer
- Section of Biomedical Genetics, Department of Medicine, Boston University School of Medicine, Boston, MA
| | - Brion Maher
- Department of Mental Health, Johns Hopkins University, Baltimore, MD
| | - Michael Vanyukov
- Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, PA
| | - Michelle Taylor
- MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, Bristol, BS, UK
| | - Jenifer J Ware
- MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, Bristol, BS, UK
| | - Marcus R Munafò
- MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, Bristol, BS, UK
| | - Sharon M Lutz
- Department of Biostatistics and Informatics, University of Colorado Anschutz Medical Campus, Aurora, CO
| | - John E Hokanson
- Department of Biostatistics and Informatics, University of Colorado Anschutz Medical Campus, Aurora, CO
| | - Fangyi Gu
- Genetic Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, United States Department of Health and Human Services, Bethesda, MD
| | - Maria T Landi
- Genetic Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, United States Department of Health and Human Services, Bethesda, MD
| | - Neil E Caporaso
- Genetic Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, United States Department of Health and Human Services, Bethesda, MD
| | - Dana B Hancock
- Behavioral Health and Criminal Justice Division, RTI International, Research Triangle Park, NC
| | - Nathan C Gaddis
- Research Computing Division, RTI International, Research Triangle Park, NC
| | - Timothy B Baker
- Center for Tobacco Research and Intervention, University of Wisconsin, Madison, WI
| | - Laura J Bierut
- Department of Psychiatry, Washington University, St. Louis, MO
| | - Eric O Johnson
- Behavioral Health and Criminal Justice Division, RTI International, Research Triangle Park, NC.,Fellow Program, RTI International, Research Triangle Park, NC
| | - Meghan Chenoweth
- Centre for Addiction and Mental Health, and Departments of Pharmacology and Toxicology, and Psychiatry, University of Toronto, Toronto, Canada
| | - Caryn Lerman
- Center for Interdisciplinary Research on Nicotine Addiction, Department of Psychiatry, University of Pennsylvania, Philadelphia, PA
| | - Rachel Tyndale
- Centre for Addiction and Mental Health, and Departments of Pharmacology and Toxicology, and Psychiatry, University of Toronto, Toronto, Canada
| | - Jaakko Kaprio
- Department of Public Health, University of Helsinki, Helsinki, FI, Finland.,Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland
| | - Xiangning Chen
- Nevada Institute of Personalized Medicine, University of Nevada Las Vegas, Las Vegas, NV.,Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.,Department of Psychology, University of Nevada Las Vegas, Las Vegas, NV
| |
Collapse
|
4
|
Bickler PE. Amplification of Snake Venom Toxicity by Endogenous Signaling Pathways. Toxins (Basel) 2020; 12:E68. [PMID: 31979014 PMCID: PMC7076764 DOI: 10.3390/toxins12020068] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 01/12/2020] [Accepted: 01/14/2020] [Indexed: 02/07/2023] Open
Abstract
The active components of snake venoms encompass a complex and variable mixture of proteins that produce a diverse, but largely stereotypical, range of pharmacologic effects and toxicities. Venom protein diversity and host susceptibilities determine the relative contributions of five main pathologies: neuromuscular dysfunction, inflammation, coagulopathy, cell/organ injury, and disruption of homeostatic mechanisms of normal physiology. In this review, we describe how snakebite is not only a condition mediated directly by venom, but by the amplification of signals dysregulating inflammation, coagulation, neurotransmission, and cell survival. Although venom proteins are diverse, the majority of important pathologic events following envenoming follow from a small group of enzyme-like activities and the actions of small toxic peptides. This review focuses on two of the most important enzymatic activities: snake venom phospholipases (svPLA2) and snake venom metalloproteases (svMP). These two enzyme classes are adept at enabling venom to recruit homologous endogenous signaling systems with sufficient magnitude and duration to produce and amplify cell injury beyond what would be expected from the direct impact of a whole venom dose. This magnification produces many of the most acutely important consequences of envenoming as well as chronic sequelae. Snake venom PLA2s and MPs enzymes recruit prey analogs of similar activity. The transduction mechanisms that recruit endogenous responses include arachidonic acid, intracellular calcium, cytokines, bioactive peptides, and possibly dimerization of venom and prey protein homologs. Despite years of investigation, the precise mechanism of svPLA2-induced neuromuscular paralysis remains incomplete. Based on recent studies, paralysis results from a self-amplifying cycle of endogenous PLA2 activation, arachidonic acid, increases in intracellular Ca2+ and nicotinic receptor deactivation. When prolonged, synaptic suppression supports the degeneration of the synapse. Interaction between endothelium-damaging MPs, sPLA2s and hyaluronidases enhance venom spread, accentuating venom-induced neurotoxicity, inflammation, coagulopathy and tissue injury. Improving snakebite treatment requires new tools to understand direct and indirect effects of envenoming. Homologous PLA2 and MP activities in both venoms and prey/snakebite victim provide molecular targets for non-antibody, small molecule agents for dissecting mechanisms of venom toxicity. Importantly, these tools enable the separation of venom-specific and prey-specific pathological responses to venom.
Collapse
Affiliation(s)
- Philip E. Bickler
- Department of Anesthesia and Perioperative Care, University of California at San Francisco, San Francisco, CA 94143-0542, USA;
- California Academy of Sciences, San Francisco, CA 94118, USA
| |
Collapse
|
5
|
Vivekanandarajah A, Waters KA, Machaalani R. Cigarette smoke exposure effects on the brainstem expression of nicotinic acetylcholine receptors (nAChRs), and on cardiac, respiratory and sleep physiologies. Respir Physiol Neurobiol 2018; 259:1-15. [PMID: 30031221 DOI: 10.1016/j.resp.2018.07.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Revised: 07/16/2018] [Accepted: 07/17/2018] [Indexed: 12/15/2022]
Abstract
Cigarette smoking during pregnancy is the largest modifiable risk factor for adverse outcomes in the infant. Investigations have focused on the psychoactive component of cigarettes, nicotine. One proposed mechanism leading to adverse effects is the interaction between nicotine and its nicotinic acetylcholine receptors (nAChRs). Much data has been generated over the past three decades on the effects of cigarette smoke exposure (CSE) on the expression of the nAChRs in the brainstem and physiological parameters related to cardiac, respiration and sleep, in the offspring of smoking mothers and animal models of nicotine exposure. This review summarises this data and discusses the main findings, highlighting that findings in animal models closely correlate with those from human studies, and that the major brainstem sites where the expression level for the nAChRs are consistently affected include those that play vital roles in cardiorespiration (hypoglossal nucleus, dorsal motor nucleus of the vagus, nucleus of the solitary tract), chemosensation (nucleus of the solitary tract, arcuate nucleus) and arousal (rostral mesopontine sites such as the locus coeruleus and nucleus pontis oralis). These findings provide evidence for the adverse effects of CSE during and after pregnancy to the infant and the need to continue with the health campaign advising against CSE.
Collapse
Affiliation(s)
- Arunnjah Vivekanandarajah
- SIDS and Sleep Apnea Laboratory, Sydney Medical School, Medical Foundation Building K25, University of Sydney, NSW 2006, Australia.
| | - Karen A Waters
- SIDS and Sleep Apnea Laboratory, Sydney Medical School, Medical Foundation Building K25, University of Sydney, NSW 2006, Australia; Discipline of Paediatrics and Child Health, Children's Hospital Westmead, NSW, Australia
| | - Rita Machaalani
- SIDS and Sleep Apnea Laboratory, Sydney Medical School, Medical Foundation Building K25, University of Sydney, NSW 2006, Australia; Discipline of Paediatrics and Child Health, Children's Hospital Westmead, NSW, Australia
| |
Collapse
|
6
|
Sugita S, Fleming LL, Wood C, Vaughan SK, Gomes MPSM, Camargo W, Naves LA, Prado VF, Prado MAM, Guatimosim C, Valdez G. VAChT overexpression increases acetylcholine at the synaptic cleft and accelerates aging of neuromuscular junctions. Skelet Muscle 2016; 6:31. [PMID: 27713817 PMCID: PMC5050580 DOI: 10.1186/s13395-016-0105-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 08/26/2016] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Cholinergic dysfunction occurs during aging and in a variety of diseases, including amyotrophic lateral sclerosis (ALS). However, it remains unknown whether changes in cholinergic transmission contributes to age- and disease-related degeneration of the motor system. Here we investigated the effect of moderately increasing levels of synaptic acetylcholine (ACh) on the neuromuscular junction (NMJ), muscle fibers, and motor neurons during development and aging and in a mouse model for amyotrophic lateral sclerosis (ALS). METHODS Chat-ChR2-EYFP (VAChTHyp) mice containing multiple copies of the vesicular acetylcholine transporter (VAChT), mutant superoxide dismutase 1 (SOD1G93A), and Chat-IRES-Cre and tdTomato transgenic mice were used in this study. NMJs, muscle fibers, and α-motor neurons' somata and their axons were examined using a light microscope. Transcripts for select genes in muscles and spinal cords were assessed using real-time quantitative PCR. Motor function tests were carried out using an inverted wire mesh and a rotarod. Electrophysiological recordings were collected to examine miniature endplate potentials (MEPP) in muscles. RESULTS We show that VAChT is elevated in the spinal cord and at NMJs of VAChTHyp mice. We also show that the amplitude of MEPPs is significantly higher in VAChTHyp muscles, indicating that more ACh is loaded into synaptic vesicles and released into the synaptic cleft at NMJs of VAChTHyp mice compared to control mice. While the development of NMJs was not affected in VAChTHyp mice, NMJs prematurely acquired age-related structural alterations in adult VAChTHyp mice. These structural changes at NMJs were accompanied by motor deficits in VAChTHyp mice. However, cellular features of muscle fibers and levels of molecules with critical functions at the NMJ and in muscle fibers were largely unchanged in VAChTHyp mice. In the SOD1G93A mouse model for ALS, increasing synaptic ACh accelerated degeneration of NMJs caused motor deficits and resulted in premature death specifically in male mice. CONCLUSIONS The data presented in this manuscript demonstrate that increasing levels of ACh at the synaptic cleft promote degeneration of adult NMJs, contributing to age- and disease-related motor deficits. We thus propose that maintaining normal cholinergic signaling in muscles will slow degeneration of NMJs and attenuate loss of motor function caused by aging and neuromuscular diseases.
Collapse
Affiliation(s)
- Satoshi Sugita
- Virginia Tech Carilion Research Institute, Virginia Tech, Roanoke, VA USA
| | - Leland L. Fleming
- Virginia Tech Carilion Research Institute, Virginia Tech, Roanoke, VA USA
- Virginia Tech Postbaccalaureate Research and Education (VT PREP) Scholar, Virginia Tech, Blacksburg, VA USA
| | - Caleb Wood
- Virginia Tech Carilion Research Institute, Virginia Tech, Roanoke, VA USA
| | - Sydney K. Vaughan
- Virginia Tech Carilion Research Institute, Virginia Tech, Roanoke, VA USA
- Graduate Program in Translational Biology, Medicine, and Health, Virginia Tech, Blacksburg, VA USA
| | - Matheus P. S. M. Gomes
- Departamento de Morfologia, Instiuto Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais Brazil
| | - Wallace Camargo
- Departamento de Fisiologia e Biofísica, Instiuto Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais Brazil
| | - Ligia A. Naves
- Departamento de Fisiologia e Biofísica, Instiuto Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais Brazil
| | - Vania F. Prado
- Robarts Research Institute, Department of Physiology and Pharmacology, Department of Anatomy & Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON N6A5K8 Canada
| | - Marco A. M. Prado
- Robarts Research Institute, Department of Physiology and Pharmacology, Department of Anatomy & Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON N6A5K8 Canada
| | - Cristina Guatimosim
- Departamento de Morfologia, Instiuto Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais Brazil
| | - Gregorio Valdez
- Virginia Tech Carilion Research Institute, Virginia Tech, Roanoke, VA USA
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA USA
| |
Collapse
|
7
|
Fu YL, Wang YJ, Mu TW. Proteostasis Maintenance of Cys-Loop Receptors. ION CHANNELS AS THERAPEUTIC TARGETS, PART A 2016; 103:1-23. [DOI: 10.1016/bs.apcsb.2015.11.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
|
8
|
Fox AM, Moonschi FH, Richards CI. The nicotine metabolite, cotinine, alters the assembly and trafficking of a subset of nicotinic acetylcholine receptors. J Biol Chem 2015; 290:24403-12. [PMID: 26269589 DOI: 10.1074/jbc.m115.661827] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Indexed: 12/27/2022] Open
Abstract
Exposure to nicotine alters the trafficking and assembly of nicotinic receptors (nAChRs), leading to their up-regulation on the plasma membrane. Although the mechanism is not fully understood, nicotine-induced up-regulation is believed to contribute to nicotine addiction. The effect of cotinine, the primary metabolite of nicotine, on nAChR trafficking and assembly has not been extensively investigated. We utilize a pH-sensitive variant of GFP, super ecliptic pHluorin, to differentiate between intracellular nAChRs and those expressed on the plasma membrane to quantify changes resulting from cotinine and nicotine exposure. Similar to nicotine, exposure to cotinine increases the number of α4β2 receptors on the plasma membrane and causes a redistribution of intracellular receptors. In contrast to this, cotinine exposure down-regulates α6β2β3 receptors. We also used single molecule fluorescence studies to show that cotinine and nicotine both alter the assembly of α4β2 receptors to favor the high sensitivity (α4)2(β2)3 stoichiometry.
Collapse
Affiliation(s)
- Ashley M Fox
- From the Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506
| | - Faruk H Moonschi
- From the Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506
| | | |
Collapse
|
9
|
Mostafa E, Storey B, Farghaly AM, Afify HAEH, Taha AAER, Wolstenholme AJ. Transient effects of levamisole on Brugia malayi microfilariae. INVERTEBRATE NEUROSCIENCE 2015; 15:5. [PMID: 26187649 DOI: 10.1007/s10158-015-0181-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Accepted: 07/09/2015] [Indexed: 11/30/2022]
Abstract
Levamisole is an anthelmintic drug that acts by activating nicotinic acetylcholine receptors at the nematode neuromuscular junction and causing paralysis. We measured the in vitro effects of levamisole on the motility of Brugia malayi microfilariae; after 2 h incubation the apparent IC50 was 2.68 mM. Lower drug concentrations, such as 1 mM, caused an immediate total paralysis that lasted for up to 1 h, but was completely reversed by 2 h of incubation. The 'recovered' parasites were still completely susceptible to application of a second nicotinic agonist, pyrantel.
Collapse
Affiliation(s)
- Eman Mostafa
- Department of Infectious Diseases, University of Georgia, 501 D.W. Brooks Drive, Athens, GA, 30602, USA
| | | | | | | | | | | |
Collapse
|
10
|
Tintignac LA, Brenner HR, Rüegg MA. Mechanisms Regulating Neuromuscular Junction Development and Function and Causes of Muscle Wasting. Physiol Rev 2015; 95:809-52. [DOI: 10.1152/physrev.00033.2014] [Citation(s) in RCA: 224] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The neuromuscular junction is the chemical synapse between motor neurons and skeletal muscle fibers. It is designed to reliably convert the action potential from the presynaptic motor neuron into the contraction of the postsynaptic muscle fiber. Diseases that affect the neuromuscular junction may cause failure of this conversion and result in loss of ambulation and respiration. The loss of motor input also causes muscle wasting as muscle mass is constantly adapted to contractile needs by the balancing of protein synthesis and protein degradation. Finally, neuromuscular activity and muscle mass have a major impact on metabolic properties of the organisms. This review discusses the mechanisms involved in the development and maintenance of the neuromuscular junction, the consequences of and the mechanisms involved in its dysfunction, and its role in maintaining muscle mass during aging. As life expectancy is increasing, loss of muscle mass during aging, called sarcopenia, has emerged as a field of high medical need. Interestingly, aging is also accompanied by structural changes at the neuromuscular junction, suggesting that the mechanisms involved in neuromuscular junction maintenance might be disturbed during aging. In addition, there is now evidence that behavioral paradigms and signaling pathways that are involved in longevity also affect neuromuscular junction stability and sarcopenia.
Collapse
Affiliation(s)
- Lionel A. Tintignac
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Hans-Rudolf Brenner
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Markus A. Rüegg
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| |
Collapse
|
11
|
Darabid H, Perez-Gonzalez AP, Robitaille R. Neuromuscular synaptogenesis: coordinating partners with multiple functions. Nat Rev Neurosci 2014; 15:630-1. [DOI: 10.1038/nrn3821] [Citation(s) in RCA: 111] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
|
12
|
Poorthuis RB, Mansvelder HD. Nicotinic acetylcholine receptors controlling attention: behavior, circuits and sensitivity to disruption by nicotine. Biochem Pharmacol 2013; 86:1089-98. [PMID: 23856288 DOI: 10.1016/j.bcp.2013.07.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 07/01/2013] [Accepted: 07/02/2013] [Indexed: 11/26/2022]
Abstract
Attention is a central cognitive function that enables long-term engagement in a task and suppression of irrelevant information to obtain future goals. The prefrontal cortex (PFC) is the main link in integrating emotional and motivational state of an animal to regulate top-down attentional processes. Acetylcholine modulates PFC neuronal networks by activating nicotinic acetylcholine receptors (nAChRs) to support attention. However, how neuronal activity changes in the PFC during attention and which nAChR subtypes mediate this is only rudimentarily understood, but progress is being made. Recently, exciting new insights were obtained in the dynamics of cholinergic signaling in the PFC and modes of acetylcholine transmission via nAChRs in the cortex. In addition, mechanisms are uncovered on how the PFC circuitry is regulated by nAChRs. Novel studies show that endogenous activation of nAChRs in the PFC plays a central role in controlling attention. Here, we review current insights into how different subtypes of nAChRs expressed by distinct types of neurons in the PFC circuitry shape attention. In addition we discuss the impact of nicotine on the cholinergic system and prefrontal cortical circuits. Low concentrations of nicotine, as experienced by smokers, interfere with cholinergic signaling. In the long-term exposure to nicotine during adolescence leads to maladaptive adaptations of the PFC circuitry, which ultimately leads to a decrement in attention performance, again emphasizing the importance of nAChRs in attention.
Collapse
Affiliation(s)
- Rogier B Poorthuis
- Department of Integrative Neurophysiology, CNCR, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
| | | |
Collapse
|
13
|
Layer-specific interference with cholinergic signaling in the prefrontal cortex by smoking concentrations of nicotine. J Neurosci 2013; 33:4843-53. [PMID: 23486955 DOI: 10.1523/jneurosci.5012-12.2013] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Adolescence is a period in which the developing prefrontal cortex (PFC) is sensitive to maladaptive changes when exposed to nicotine. Nicotine affects PFC function and repeated exposure to nicotine during adolescence impairs attention performance and impulse control during adulthood. Nicotine concentrations experienced by smokers are known to desensitize nicotinic acetylcholine receptors (nAChRs), but the impact thereof on PFC circuits is poorly understood. Here, we investigated how smoking concentrations of nicotine (100-300 nm) interfere with cholinergic signaling in the mouse PFC. nAChR desensitization depends on subunit composition. Since nAChR subunits are differentially expressed across layers of the PFC neuronal network, we hypothesized that cholinergic signaling through nAChRs across layers would suffer differentially from exposure to nicotine. Throughout the PFC, nicotine strongly desensitized responses to ACh in neurons expressing β2* nAChRs, whereas ACh responses mediated by α7 nAChRs were not hampered. The amount of desensitization of β2* nAChR currents depended on neuron type and cortical layer. β2*-mediated responses of interneurons in LII-III and LVI completely desensitized, while cholinergic responses in LV interneurons and LVI pyramidal cells showed less desensitization. This discrepancy depended on α5 subunit expression. Two-photon imaging of neuronal population activity showed that prolonged exposure to nicotine limited cholinergic signaling through β2* nAChRs to deep PFC layers where α5 subunits were expressed. Together, our results demonstrate a layer-dependent decrease in cholinergic activation of the PFC through nAChRs by nicotine. These mechanisms may be one of the first steps leading up to the pathophysiological changes associated with nicotine exposure during adolescence.
Collapse
|
14
|
Thompson AJ. Recent developments in 5-HT3 receptor pharmacology. Trends Pharmacol Sci 2013; 34:100-9. [DOI: 10.1016/j.tips.2012.12.002] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Revised: 12/07/2012] [Accepted: 12/10/2012] [Indexed: 12/19/2022]
|
15
|
Kroker KS, Rast G, Rosenbrock H. Differential effects of subtype-specific nicotinic acetylcholine receptor agonists on early and late hippocampal LTP. Eur J Pharmacol 2011; 671:26-32. [PMID: 21968142 DOI: 10.1016/j.ejphar.2011.09.167] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Revised: 09/13/2011] [Accepted: 09/15/2011] [Indexed: 01/14/2023]
Abstract
Brain nicotinic acetylcholine receptors are involved in several neuropsychiatric disorders, e.g. Alzheimer's and Parkinson's diseases, Tourette's syndrome, schizophrenia, depression, autism, attention deficit hyperactivity disorder, and anxiety. Currently, approaches selectively targeting the activation of specific nicotinic acetylcholine receptors are in clinical development for treatment of memory impairment of Alzheimer's disease patients. These are α4β2 and α7 nicotinic acetylcholine receptor agonists which are believed to enhance cholinergic and glutamatergic neurotransmission, respectively. In order to gain a better insight into the mechanistic role of these two nicotinic acetylcholine receptors in learning and memory, we investigated the effects of the α4β2 nicotinic acetylcholine receptor agonist TC-1827 and the α7 nicotinic acetylcholine receptor partial agonist SSR180711 on hippocampal long-term potentiation (LTP), a widely accepted cellular experimental model of memory formation. Generally, LTP is distinguished in an early and a late form, the former being protein-synthesis independent and the latter being protein-synthesis dependent. TC-1827 was found to increase early LTP in a bell-shaped dose dependent manner, but did not affect late LTP. In contrast, the α7 nicotinic acetylcholine receptor partial agonist SSR180711 showed enhancing effects on both early and late LTP in a bell-shaped manner. Furthermore, SSR180711 not only increased early LTP, but also transformed it into late LTP, which was not observed with the α4β2 nicotinic acetylcholine receptor agonist. Therefore, based on these findings α7 nicotinic acetylcholine receptor (partial) agonists appear to exhibit stronger efficacy on memory improvement than α4β2 nicotinic acetylcholine receptor agonists.
Collapse
Affiliation(s)
- Katja S Kroker
- Boehringer Ingelheim Pharma GmbH & Co KG, Department of CNS Diseases Research, Birkendorfer Strasse 65, 88397 Biberach, Germany.
| | | | | |
Collapse
|
16
|
Borroni V, Barrantes FJ. Cholesterol modulates the rate and mechanism of acetylcholine receptor internalization. J Biol Chem 2011; 286:17122-32. [PMID: 21357688 DOI: 10.1074/jbc.m110.211870] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Stability of the nicotinic acetylcholine receptor (AChR) at the cell surface is key to the correct functioning of the cholinergic synapse. Cholesterol (Chol) is necessary for homeostasis of AChR levels at the plasmalemma and for ion translocation. Here we characterize the endocytic pathway followed by muscle-type AChR in Chol-depleted cells (Chol(-)). Under such conditions, the AChR is internalized by a ligand-, clathrin-, and dynamin-independent mechanism. Expression of a dominant negative form of the small GTPase Rac1, Rac1N17, abolishes receptor endocytosis. Unlike the endocytic pathway in control CHO cells (1), accelerated AChR internalization proceeds even upon disruption of the actin cytoskeleton. Under Chol(-) conditions, AChR internalization is furthermore found to require the activity of Arf6 and its effectors Rac1 and phospholipase D. The Arf6-dependent mechanism may constitute the default endocytic pathway followed by the AChR in the absence of external ligands, membrane Chol levels acting as a key homeostatic regulator of cell surface receptor levels.
Collapse
Affiliation(s)
- Virginia Borroni
- Instituto Investigaciones Bioquímicas de Bahía Blanca, C Carrindanga Km 7, B8000FWB Bahía Blanca, Argentina
| | | |
Collapse
|
17
|
Bernareggi A, Reyes-Ruiz JM, Lorenzon P, Ruzzier F, Miledi R. Microtransplantation of acetylcholine receptors from normal or denervated rat skeletal muscles to frog oocytes. J Physiol 2011; 589:1133-42. [PMID: 21224230 DOI: 10.1113/jphysiol.2010.202994] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Cell membranes, carrying neurotransmitter receptors and ion channels, can be 'microtransplanted' into frog oocytes. This technique allows a direct functional characterization of the original membrane proteins, together with any associated molecules they may have, still embedded in their natural lipid environment. This approach has been previously demonstrated to be very useful to study neurotransmitter receptors and ion channels contained in cell membranes isolated from human brains. Here, we examined the possibility of using the microtransplantation method to study acetylcholine receptors from normal and denervated rat skeletal muscles. We found that the muscle membranes, carrying their fetal or adult acetylcholine receptor isoforms, could be efficiently microtransplanted to the oocyte membrane, making the oocytes become sensitive to acetylcholine. These results show that oocytes injected with skeletal muscle membranes efficiently incorporate functional acetylcholine receptors, thus making the microtransplantation approach a valuable tool to further investigate receptors and ion channels of human muscle diseases.
Collapse
Affiliation(s)
- Annalisa Bernareggi
- Department of Life Sciences, University of Trieste, Via A. Fleming 22, I-34127 Trieste, Italy.
| | | | | | | | | |
Collapse
|
18
|
Shi L, Butt B, Ip FCF, Dai Y, Jiang L, Yung WH, Greenberg ME, Fu AKY, Ip NY. Ephexin1 is required for structural maturation and neurotransmission at the neuromuscular junction. Neuron 2010; 65:204-16. [PMID: 20152127 DOI: 10.1016/j.neuron.2010.01.012] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/24/2009] [Indexed: 12/24/2022]
Abstract
The maturation of neuromuscular junctions (NMJs) requires the topological transformation of postsynaptic acetylcholine receptor (AChR)-containing structures from a simple plaque to an elaborate structure composed of pretzel-like branches. This maturation process results in the precise apposition of the presynaptic and postsynaptic specializations. However, little is known about the molecular mechanisms underlying the plaque-to-pretzel transition of AChR clusters. In this study, we identify an essential role for the RhoGEF ephexin1 in the maturation of AChR clusters. Adult ephexin1(-/-) mice exhibit severe muscle weakness and impaired synaptic transmission at the NMJ. Intriguingly, when ephexin1 expression is deficient in vivo, the NMJ fails to mature into the pretzel-like shape, and such abnormalities can be rescued by re-expression of ephexin1. We further demonstrate that ephexin1 regulates the stability of AChR clusters in a RhoA-dependent manner. Taken together, our findings reveal an indispensible role for ephexin1 in regulating the structural maturation and neurotransmission of NMJs.
Collapse
Affiliation(s)
- Lei Shi
- Department of Biochemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China
| | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Abstract
Nicotinic acetylcholine receptors (nAChRs) play critical roles throughout the body. Precise regulation of the cellular location and availability of nAChRs on neurons and target cells is critical to their proper function. Dynamic, post-translational regulation of nAChRs, particularly control of their movements among the different compartments of cells, is an important aspect of that regulation. A combination of new information and new techniques has the study of nAChR trafficking poised for new breakthroughs.
Collapse
|
20
|
Kordosky-Herrera K, Grow WA. Caffeine and nicotine decrease acetylcholine receptor clustering in C2C12 myotube culture. Cell Tissue Res 2008; 335:341-8. [DOI: 10.1007/s00441-008-0691-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2008] [Accepted: 08/28/2008] [Indexed: 11/24/2022]
|
21
|
Kumari S, Borroni V, Chaudhry A, Chanda B, Massol R, Mayor S, Barrantes FJ. Nicotinic acetylcholine receptor is internalized via a Rac-dependent, dynamin-independent endocytic pathway. J Cell Biol 2008; 181:1179-93. [PMID: 18591431 PMCID: PMC2442195 DOI: 10.1083/jcb.200709086] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2007] [Accepted: 05/30/2008] [Indexed: 01/15/2023] Open
Abstract
Endocytosis of the nicotinic acetylcholine receptor (AChR) is a proposed major mechanism of neuromodulation at neuromuscular junctions and in the pathology of synapses in the central nervous system. We show that binding of the competitive antagonist alpha-bungarotoxin (alphaBTX) or antibody-mediated cross-linking induces the internalization of cell surface AChR to late endosomes when expressed heterologously in Chinese hamster ovary cells or endogenously in C2C12 myocytes. Internalization occurs via sequestration of AChR-alphaBTX complexes in narrow, tubular, surface-connected compartments, which are indicated by differential surface accessibility of fluorescently tagged alphaBTX-AChR complexes to small and large molecules and real-time total internal reflection fluorescence imaging. Internalization occurs in the absence of clathrin, caveolin, or dynamin but requires actin polymerization. alphaBTX binding triggers c-Src phosphorylation and subsequently activates the Rho guanosine triphosphatase Rac1. Consequently, inhibition of c-Src kinase activity, Rac1 activity, or actin polymerization inhibits internalization via this unusual endocytic mechanism. This pathway may regulate AChR levels at ligand-gated synapses and in pathological conditions such as the autoimmune disease myasthenia gravis.
Collapse
Affiliation(s)
- Sudha Kumari
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
| | | | | | | | | | | | | |
Collapse
|
22
|
Milholland RBR, Gordon H. A role for acetylcholine receptors in their own aggregation on muscle cells. Dev Neurobiol 2007; 67:999-1008. [PMID: 17565711 DOI: 10.1002/dneu.20385] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Both neurotrophic factors and activity regulate synaptogenesis. At neuromuscular synapses, the neural factor agrin released from motor neuron terminals stimulates postsynaptic specialization by way of the muscle specific kinase MuSK. In addition, activity through acetylcholine receptors (AChRs) has been implicated in the stabilization of pre- and postsynaptic contacts on muscle at various stages of development. We show here that activation of AChRs with specific concentrations of nicotine is sufficient to induce AChR aggregation and that this induction requires the function of L-type calcium channels (L-CaChs). Furthermore, AChR function is required for agrin induced AChR aggregation in C2 muscle cells. The same concentrations of nicotine did not induce observable tyrosine phosphorylation on either MuSK or the AChR beta subunit, suggesting significant differences between the mechanisms of agrin and activity induced aggregation. The AChR/L-CaCh pathway provides a mechanism by which neuromuscular signal transmission can act in concert with the agrin-MuSK signaling cascade to regulate NMJ formation.
Collapse
Affiliation(s)
- Rebecca B R Milholland
- Department of Cell Biology and Anatomy, University of Arizona Health Sciences Center, Tucson, Arizona 85724-5044, USA
| | | |
Collapse
|
23
|
Kummer TT, Misgeld T, Sanes JR. Assembly of the postsynaptic membrane at the neuromuscular junction: paradigm lost. Curr Opin Neurobiol 2006; 16:74-82. [PMID: 16386415 DOI: 10.1016/j.conb.2005.12.003] [Citation(s) in RCA: 236] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Accepted: 12/15/2005] [Indexed: 11/28/2022]
Abstract
Studies of the vertebrate skeletal neuromuscular junction led to an influential model of how neurotransmitter receptors accumulate in the postsynaptic membrane. In this model, motor axons organize postsynaptic development by secreting neuregulin to induce acetylcholine receptor gene transcription in specialized subsynaptic nuclei, agrin to cluster diffuse receptors in the postsynaptic membrane, and acetylcholine to evoke electrical activity that promotes synaptic maturation. However, new studies in this area have first, demonstrated that axons sometimes innervate pre-existing receptor clusters; second, recast the roles of agrin and neuregulin; third, revealed early effects of neurotransmission; fourth, questioned the role of subsynaptic myonuclei; fifth, shown that elaborately-branched postsynaptic structures can form aneurally; and sixth, raised the possibility that neurotransmitter affects receptor type as well as distribution. These recent studies challenge the widely-held paradigms, although not the results that led to them, and suggest a new model for neuromuscular synaptogenesis.
Collapse
Affiliation(s)
- Terrance T Kummer
- Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA
| | | | | |
Collapse
|
24
|
Bruneau E, Sutter D, Hume RI, Akaaboune M. Identification of nicotinic acetylcholine receptor recycling and its role in maintaining receptor density at the neuromuscular junction in vivo. J Neurosci 2006; 25:9949-59. [PMID: 16251443 PMCID: PMC6725561 DOI: 10.1523/jneurosci.3169-05.2005] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In the CNS, receptor recycling is critical for synaptic plasticity; however, the recycling of receptors has never been observed at peripheral synapses. Using a novel imaging technique, we show here that nicotinic acetylcholine receptors (AChRs) recycle into the postsynaptic membrane of the neuromuscular junction. By sequentially labeling AChRs with biotin-bungarotoxin and streptavidin-fluorophore conjugates, we were able to distinguish recycled, preexisting, and new receptor pools at synapses in living mice. Time-lapse imaging revealed that recycled AChRs were incorporated into the synapse within hours of initial labeling, and their numbers increased with time. At fully functional synapses, AChR recycling was robust and comparable in magnitude with the insertion of newly synthesized receptors, whereas chronic synaptic activity blockade nearly abolished receptor recycling. Finally, using the same sequential labeling method, we found that acetylcholinesterase, another synaptic component, does not recycle. These results identify an activity-dependent AChR-recycling mechanism that enables the regulation of receptor density, which could lead to rapid alterations in synaptic efficacy.
Collapse
Affiliation(s)
- Emile Bruneau
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA
| | | | | | | |
Collapse
|
25
|
Misgeld T, Kummer TT, Lichtman JW, Sanes JR. Agrin promotes synaptic differentiation by counteracting an inhibitory effect of neurotransmitter. Proc Natl Acad Sci U S A 2005; 102:11088-93. [PMID: 16043708 PMCID: PMC1182450 DOI: 10.1073/pnas.0504806102] [Citation(s) in RCA: 168] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synaptic organizing molecules and neurotransmission regulate synapse development. Here, we use the skeletal neuromuscular junction to assess the interdependence of effects evoked by an essential synaptic organizing protein, agrin, and the neuromuscular transmitter, acetylcholine (ACh). Mice lacking agrin fail to maintain neuromuscular junctions, whereas neuromuscular synapses differentiate extensively in the absence of ACh. We now demonstrate that agrin's action in vivo depends critically on cholinergic neurotransmission. Using double-mutant mice, we show that synapses do form in the absence of agrin provided that ACh is also absent. We provide evidence that ACh destabilizes nascent postsynaptic sites, and that one major physiological role of agrin is to counteract this "antisynaptogenic" influence. Similar interactions between neurotransmitters and synaptic organizing molecules may operate at synapses in the central nervous system.
Collapse
Affiliation(s)
- Thomas Misgeld
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
| | | | | | | |
Collapse
|
26
|
Scearce-Levie K, Lieberman MD, Elliott HH, Conklin BR. Engineered G protein coupled receptors reveal independent regulation of internalization, desensitization and acute signaling. BMC Biol 2005; 3:3. [PMID: 15707483 PMCID: PMC551613 DOI: 10.1186/1741-7007-3-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2004] [Accepted: 02/11/2005] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND The physiological regulation of G protein-coupled receptors, through desensitization and internalization, modulates the length of the receptor signal and may influence the development of tolerance and dependence in response to chronic drug treatment. To explore the importance of receptor regulation, we engineered a series of Gi-coupled receptors that differ in signal length, degree of agonist-induced internalization, and ability to induce adenylyl cyclase superactivation. All of these receptors, based on the kappa opioid receptor, were modified to be receptors activated solely by synthetic ligands (RASSLs). This modification allows us to compare receptors that have the same ligands and effectors, but differ only in desensitization and internalization. RESULTS Removal of phosphorylation sites in the C-terminus of the RASSL resulted in a mutant that was resistant to internalization and less prone to desensitization. Replacement of the C-terminus of the RASSL with the corresponding portion of the mu opioid receptor eliminated the induction of AC superactivation, without disrupting agonist-induced desensitization or internalization. Surprisingly, removal of phosphorylation sites from this chimera resulted in a receptor that is constitutively internalized, even in the absence of agonist. However, the receptor still signals and desensitizes in response to agonist, indicating normal G-protein coupling and partial membrane expression. CONCLUSIONS These studies reveal that internalization, desensitization and adenylyl cyclase superactivation, all processes that decrease chronic Gi-receptor signals, are independently regulated. Furthermore, specific mutations can radically alter superactivation or internalization without affecting the efficacy of acute Gi signaling. These mutant RASSLs will be useful for further elucidating the temporal dynamics of the signaling of G protein-coupled receptors in vitro and in vivo.
Collapse
Affiliation(s)
- Kimberly Scearce-Levie
- The Gladstone Institute of Neurological Disease and the Gladstone Institute of Cardiovascular Disease, San Francisco CA 94158 USA
| | - Michael D Lieberman
- The Gladstone Institute of Neurological Disease and the Gladstone Institute of Cardiovascular Disease, San Francisco CA 94158 USA
| | - Heather H Elliott
- The Gladstone Institute of Neurological Disease and the Gladstone Institute of Cardiovascular Disease, San Francisco CA 94158 USA
| | - Bruce R Conklin
- The Gladstone Institute of Neurological Disease and the Gladstone Institute of Cardiovascular Disease, San Francisco CA 94158 USA
- Departments of Medicine and Molecular and Cellular Pharmacology, University of California, San Francisco, CA, 94143 USA
| |
Collapse
|
27
|
|
28
|
Ilegems E, Pick HM, Deluz C, Kellenberger S, Vogel H. Noninvasive Imaging of 5-HT3 Receptor Trafficking in Live Cells. J Biol Chem 2004; 279:53346-52. [PMID: 15452106 DOI: 10.1074/jbc.m407467200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Sequential stages in the life cycle of the ionotropic 5-HT(3) receptor (5-HT(3)R) were resolved temporally and spatially in live cells by multicolor fluorescence confocal microscopy. The insertion of the enhanced cyan fluorescent protein into the large intracellular loop delivered a fluorescent 5-HT(3)R fully functional in terms of ligand binding specificity and channel activity, which allowed for the first time a complete real-time visualization and documentation of intracellular biogenesis, membrane targeting, and ligand-mediated internalization of a receptor belonging to the ligand-gated ion channel superfamily. Fluorescence signals of newly expressed receptors were detectable in the endoplasmic reticulum about 3 h after transfection onset. At this stage receptor subunits assembled to form active ligand binding sites as demonstrated in situ by binding of a fluorescent 5-HT(3)R-specific antagonist. After novel protein synthesis was chemically blocked, the 5-HT(3) R populations in the endoplasmic reticulum and Golgi cisternae moved virtually quantitatively to the cell surface, indicating efficient receptor folding and assembly. Intracellular 5-HT(3) receptors were trafficking in vesicle-like structures along microtubules to the cell surface at a velocity generally below 1 mum/s and were inserted into the plasma membrane in a characteristic cluster distribution overlapping with actin-rich domains. Internalization of cell surface 5-HT(3) receptors was observed within minutes after exposure to an extracellular agonist. Our orchestrated use of spectrally distinguishable fluorescent labels for the receptor, its cognate ligand, and specific organelle markers can be regarded as a general approach allowing subcellular insights into dynamic processes of membrane receptor trafficking.
Collapse
Affiliation(s)
- Erwin Ilegems
- Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology, CH-1015 Lausanne, Switzerland
| | | | | | | | | |
Collapse
|
29
|
Gadea A, López E, López-Colomé AM. Glutamate-induced inhibition of D-aspartate uptake in Müller glia from the retina. Neurochem Res 2004; 29:295-304. [PMID: 14992289 DOI: 10.1023/b:nere.0000010458.45085.e8] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Müller glial cells from the retina "in situ" and in primary culture, mainly express the high-affinity sodium-coupled glutamate/aspartate transporter GLAST-1, which dominates total retinal glutamate (Glu) uptake, suggesting a major role for these cells in the modulation of excitatory transmission. The possible involvement of ionotropic and metabotropic Glu receptors in the regulation of Glu uptake was studied in primary cultures of Müller glia. We demonstrate that exposure to 1 mM L-Glu induces a time-dependent inhibition of D-aspartate (D-Asp) uptake in a Na+-dependent manner, as a result of a reduction in the number of transporters at the plasma membrane. The inhibition of D-Asp uptake by Glu was not mimicked by agonists or modified by antagonists of ionotropic and metabotropic Glu receptors. In contrast, transport was inhibited by GLAST-1 transportable substrates threo-hydroxyaspartate and aspartate-beta-hydroxamate, but not by the nontransportable inhibitors trans-pyrrolidine dicarboxylate or DL-threo-beta-benzyloxyaspartic acid. Under the same experimental conditions, L-Glu did not affect the sodium-dependent transport systems for glycine or GABA. The present results demonstrate that the specific downregulation of glutamate/aspartate transport by L-Glu is unrelated to Glu receptor activation, and results from the internalization of transporter proteins triggered by the transport process itself. Such negative feedback of Glu on Glu transport, could contribute to retinal toxicity under pathological conditions in which high extracellular concentrations of Glu are reached.
Collapse
Affiliation(s)
- Ana Gadea
- Instituto de Fisiología Celular, Departamento de Neurociencias, UNAM, México, DF, México
| | | | | |
Collapse
|
30
|
Ferayorni AJ, Gunville CF, Grow WA. Nicotine decreases agrin signaling and acetylcholine receptor clustering in C2C12 myotube culture. ACTA ACUST UNITED AC 2004; 60:51-60. [PMID: 15188272 DOI: 10.1002/neu.20012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The clustering of acetylcholine receptors (AChRs) in skeletal muscle fibers is a critical event in neuromuscular synaptogenesis. AChRs in concert with other molecules form postsynaptic scaffolds in response to agrin released from motor neurons as motor neurons near skeletal muscle fibers in development. Agrin drives an intracellular signaling pathway that precedes AChR clustering and includes the tyrosine phosphorylation of AChRs. In C2C12 myotube culture, agrin application stimulates the agrin signaling pathway and AChR clustering. Previous studies have determined that the frequency of spontaneous AChR clustering is decreased and AChRs are partially inactivated when bound by the acetylcholine agonist nicotine. We hypothesized that nicotine interferes with AChR clustering and consequent postsynaptic scaffold formation. In the present study, C2C12 myoblasts were cultured with growth medium to stimulate proliferation and then differentiation medium to stimulate fusion into myotubes. They were bathed in a physiologically relevant concentration of nicotine and then subject to agrin treatment after myotube formation. Our results demonstrate that nicotine decreases agrin-induced tyrosine phosphorylation of AChRs and decreases the frequency of spontaneous as well as agrin-induced AChR clustering. We conclude that nicotine interferes with postsynaptic scaffold formation by preventing the tyrosine phosphorylation of AChRs, an agrin signaling event that precedes AChR clustering.
Collapse
Affiliation(s)
- Angelique J Ferayorni
- Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, 85308, USA
| | | | | |
Collapse
|
31
|
Nesti E, Everill B, Morielli AD. Endocytosis as a mechanism for tyrosine kinase-dependent suppression of a voltage-gated potassium channel. Mol Biol Cell 2004; 15:4073-88. [PMID: 15215309 PMCID: PMC515342 DOI: 10.1091/mbc.e03-11-0788] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The voltage-gated potassium channel Kv1.2 undergoes tyrosine phosphorylation-dependent suppression of its ionic current. However, little is known about the physical mechanism behind that process. We have found that the Kv1.2 alpha-subunit protein undergoes endocytosis in response to the same stimuli that evoke suppression of Kv1.2 ionic current. The process is tyrosine phosphorylation-dependent because the same tyrosine to phenylalanine mutation in the N-terminus of Kv1.2 that confers resistance to channel suppression (Y132F) also confers resistance to channel endocytosis. Overexpression of a dominant negative form of dynamin blocked stimulus-induced Kv1.2 endocytosis and also blocked suppression of Kv1.2 ionic current. These data indicate that endocytosis of Kv1.2 from the cell surface is a key mechanism for channel suppression by tyrosine kinases.
Collapse
Affiliation(s)
- Edmund Nesti
- The University of Vermont College of Medicine, Burlington, VT 05405, USA
| | | | | |
Collapse
|
32
|
Blanpied TA, Ehlers MD. Microanatomy of dendritic spines: emerging principles of synaptic pathology in psychiatric and neurological disease. Biol Psychiatry 2004; 55:1121-7. [PMID: 15184030 DOI: 10.1016/j.biopsych.2003.10.006] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2003] [Revised: 10/03/2003] [Accepted: 10/08/2003] [Indexed: 11/26/2022]
Abstract
Psychiatric and neurologic disorders ranging from mental retardation to addiction are accompanied by structural and functional alterations of synaptic connections in the brain. Such alterations include abnormal density and morphology of dendritic spines, synapse loss, and aberrant synaptic signaling and plasticity. Recent work is revealing an unexpectedly complex biochemical and subcellular organization of dendritic spines. In this review, we highlight the molecular interplay between functional domains of the spine, including the postsynaptic density, the actin cytoskeleton, and membrane trafficking domains. This research points to an emerging level of analysis--a microanatomical understanding of synaptic physiology--that will be critical for discerning how synapses operate in normal physiologic states and for identifying and reversing microscopic changes in psychiatric and neurologic disease.
Collapse
Affiliation(s)
- Thomas A Blanpied
- Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA
| | | |
Collapse
|
33
|
Kummer TT, Misgeld T, Lichtman JW, Sanes JR. Nerve-independent formation of a topologically complex postsynaptic apparatus. ACTA ACUST UNITED AC 2004; 164:1077-87. [PMID: 15037598 PMCID: PMC2172060 DOI: 10.1083/jcb.200401115] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
As the mammalian neuromuscular junction matures, its acetylcholine receptor (AChR)–rich postsynaptic apparatus is transformed from an oval plaque into a pretzel-shaped array of branches that precisely mirrors the branching pattern of the motor nerve terminal. Although the nerve has been believed to direct postsynaptic maturation, we report here that myotubes cultured aneurally on matrix-coated substrates form elaborately branched AChR-rich domains remarkably similar to those seen in vivo. These domains share several characteristics with the mature postsynaptic apparatus, including colocalization of multiple postsynaptic markers, clustering of subjacent myonuclei, and dependence on the muscle-specific kinase and rapsyn for their formation. Time-lapse imaging showed that branched structures arise from plaques by formation and fusion of AChR-poor perforations through a series of steps mirroring that seen in vivo. Multiple fluorophore imaging showed that growth occurs by circumferential, asymmetric addition of AChRs. Analysis in vivo revealed similar patterns of AChR addition during normal development. These results reveal the sequence of steps by which a topologically complex domain forms on a cell and suggest an unexpected nerve-independent role for the postsynaptic cell in generating this topological complexity.
Collapse
Affiliation(s)
- Terrance T Kummer
- Dept. of Anatomy and Neurobiology, Washington University School of Medicine, 660 South Euclid Ave., St. Louis, MO 63110, USA
| | | | | | | |
Collapse
|
34
|
Fujita M, Al-Tikriti MS, Tamagnan G, Zoghbi SS, Bozkurt A, Baldwin RM, Innis RB. Influence of acetylcholine levels on the binding of a SPECT nicotinic acetylcholine receptor ligand [123I]5-I-A-85380. Synapse 2003; 48:116-22. [PMID: 12645036 DOI: 10.1002/syn.10194] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although in vitro theory indicates that ligand binding is sensitive to competition with neurotransmitters, only some imaging ligands have shown such competition in vivo. The purpose of this study was to determine whether increases in acetylcholine (ACh) levels induced by an acetylcholinesterase inhibitor, physostigmine, inhibit in vivo binding of [(123)I]5-iodo-3-(2(S)-2-azetidinyl-methoxy) pyridine (5-I-A-85380), a single photon emission computed tomography ligand for the high-affinity type nicotinic ACh receptor (nAChR). Baboons were used for seven studies with a bolus plus constant infusion equilibrium paradigm. After achieving equilibrium at 5 h, physostigmine (0.02 (n = 1), 0.067 (n = 3), and 0.2 (n = 3) mg/kg) was administered intravenously and data were acquired for up to 8 h. To confirm equilibrium conditions, [(123)I]5-I-A-85380 plasma levels were measured in four studies, including all studies with 0.2 mg/kg physostigmine. Prior to physostigmine administration, thalamic activities were stable, with changes of 1.1%/h or less, except in one study with a gradual increase of 4.2%/h. Thalamic activities were decreased by 15% in one study with 0.067 mg/kg and 14-17% in all studies with 0.2 mg/kg physostigmine administration (P = 0.009). In these studies with 0.2 mg/kg physostigmine administration, [(123)I]5-I-A-85380 plasma levels showed a transient or a sustained increase after physostigmine administration that would have increased thalamic activities. These results suggest that elevated ACh levels induced by physostigmine can effectively compete in vivo with [(123)I]5-I-A-85380 binding at nAChRs. However, decreased thalamic activities could have been caused by other mechanisms, including internalization of the receptor with an associated decreased affinity for radioligand.
Collapse
Affiliation(s)
- Masahiro Fujita
- Department of Psychiatry, Yale University and VA Connecticut HCS, West Haven, Connecticut, USA.
| | | | | | | | | | | | | |
Collapse
|
35
|
Abstract
Agonist-induced internalization followed by subsequent return to the cell surface regulates G-protein-coupled receptor (GPCR) activity. Because the cellular responsiveness to ligand depends on the balance between receptor degradation and recycling, it is crucial to identify the molecules involved in GPCR recovery to the cell surface. In this study, we identify mechanisms involved in the recycling of the M4 subtype of muscarinic acetylcholine receptor. M4 is highly expressed in the CNS, plays a role in locomotor activity, and is a novel therapeutic target for neurologic and psychiatric disorders. Previous studies show that, after cholinergic stimulation, M4 internalizes from the cell surface to endosomes in cell culture and the rat brain. Here, we show that, after activation, M4 traffics to transferrin receptor- and Rab11a-positive perinuclear endosomes. Expression of the constitutively GDP-bound, inactive mutant Rab11aS25N inhibits M4 trafficking to recycling endosomes. Expression of the C-terminal tail of myosin Vb, a Rab11a effector, enhances M4 accumulation in perinuclear endosomes. Both Rab11aS25N and the myosin Vb tail impair M4 recycling. The results demonstrate that GPCR recycling is mediated through a discrete pathway using both Rab11a and myosin Vb.
Collapse
|