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Ruparelia A, Pearn ML, Mobley WC. Cognitive and pharmacological insights from the Ts65Dn mouse model of Down syndrome. Curr Opin Neurobiol 2012; 22:880-6. [PMID: 22658745 PMCID: PMC3434300 DOI: 10.1016/j.conb.2012.05.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2012] [Accepted: 05/03/2012] [Indexed: 02/06/2023]
Abstract
Down syndrome (DS) is a multi-faceted condition resulting in the most common genetic form of intellectual disability. Mouse models of DS, especially the Ts65Dn model, have been pivotal in furthering our understanding of the genetic, molecular and neurobiological mechanisms that underlie learning and memory impairments in DS. Cognitive and pharmacological insights from the Ts65Dn mouse model have led to remarkable translational progress in the development of therapeutic targets and in the emergence of DS clinical trials. Unravelling the pathogenic role of trisomic genes on human chromosome 21 and the genotype-phenotype relationship still remains a pertinent goal for tackling cognitive deficits in DS.
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Affiliation(s)
- Aarti Ruparelia
- Department of Neurodegenerative Disease, UCL Institute of Neurology, London, WC1N 3BG, UK
| | - Matthew L Pearn
- Department of Anaesthesiology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
- VA San Diego Healthcare System, 3350 La Jolla Village Drive 9125, San Diego, CA 92161-9125, USA
| | - William C Mobley
- Department of Neurosciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
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Deficits in cognition and synaptic plasticity in a mouse model of Down syndrome ameliorated by GABAB receptor antagonists. J Neurosci 2012; 32:9217-27. [PMID: 22764230 DOI: 10.1523/jneurosci.1673-12.2012] [Citation(s) in RCA: 129] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Cognitive impairment in Down syndrome (DS) is characterized by deficient learning and memory. Mouse genetic models of DS exhibit impaired cognition in hippocampally mediated behavioral tasks and reduced synaptic plasticity of hippocampal pathways. Enhanced efficiency of GABAergic neurotransmission was implicated in those changes. We have recently shown that signaling through postsynaptic GABA(B) receptors is significantly increased in the dentate gyrus of Ts65Dn mice, a genetic model of DS. Here we examined a role for GABA(B) receptors in cognitive deficits in DS by defining the effect of selective GABA(B) receptor antagonists on behavior and synaptic plasticity of adult Ts65Dn mice. Treatment with the GABA(B) receptor antagonist CGP55845 restored memory of Ts65Dn mice in the novel place recognition, novel object recognition, and contextual fear conditioning tasks, but did not affect locomotion and performance in T-maze. The treatment increased hippocampal levels of brain-derived neurotrophic factor, equally in 2N and Ts65Dn mice. In hippocampal slices, treatment with the GABA(B) receptor antagonists CGP55845 or CGP52432 enhanced long-term potentiation (LTP) in the Ts65Dn DG. The enhancement of LTP was accompanied by an increase in the NMDA receptor-mediated component of the tetanus-evoked responses. These findings are evidence for a contribution of GABA(B) receptors to changes in hippocampal-based cognition in the Ts65Dn mouse. The ability to rescue cognitive performance through treatment with selective GABA(B) receptor antagonists motivates studies to further explore the therapeutic potential of these compounds in people with DS.
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Herault Y, Duchon A, Velot E, Maréchal D, Brault V. The in vivo Down syndrome genomic library in mouse. PROGRESS IN BRAIN RESEARCH 2012; 197:169-97. [PMID: 22541293 DOI: 10.1016/b978-0-444-54299-1.00009-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Mouse models are key elements to better understand the genotype-phenotype relationship and the physiopathology of Down syndrome (DS). Even though the mouse will never recapitulate the whole spectrum of intellectual disabilities observed in the DS, mouse models have been developed over the recent decades and have been used extensively to identify homologous genes or entire regions homologous to the human chromosome 21 (Hsa21) that are necessary or sufficient to induce DS cognitive features. In this chapter, we review the principal mouse DS models which have been selected and engineered over the years either for large genomic regions or for a few or a single gene of interest. Their analyses highlight the complexity of the genetic interactions that are involved in DS cognitive phenotypes and also strengthen the hypothesis on the multigenic nature of DS. This review also addresses future research challenges relative to the making of new models and their combination to go further in the characterization of candidates and modifier of the DS features.
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Affiliation(s)
- Yann Herault
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Translational medicine and Neurogenetics program, IGBMC, CNRS, INSERM, Université de Strasbourg, UMR7104, UMR964, Illkirch, Strasbourg, France.
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Möhler H. Cognitive enhancement by pharmacological and behavioral interventions: the murine Down syndrome model. Biochem Pharmacol 2012; 84:994-9. [PMID: 22898099 DOI: 10.1016/j.bcp.2012.06.028] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Revised: 06/29/2012] [Accepted: 06/29/2012] [Indexed: 12/26/2022]
Abstract
The cognitive deficits in Down syndrome (DS) are attributed to an excessive hippocampal inhibition, which obstructs neuronal plasticity and normal learning and memory, a view which is largely based on studies of Ts65Dn mice, the best characterized mouse model of DS. The cognitive behavioral deficits of Ts65Dn mice can be rescued by reducing GABAergic inhibition, most selectively by partial inverse agonists acting on α(5) GABA-A receptors, of which one compound has recently entered clinical trials in DS. Most remarkably, the improved cognitive performance of Ts65Dn can persist for weeks and months after cessation of drug treatment, as demonstrated for the non-specific GABA antagonist pentylenetetrazole. The Alzheimer drugs, memantine and donepezil largely fail to show any benefit. Finally, repeated non-invasive sensory stimulation such as over-training or enriching the environment, are able to enhance the learning performance which underlines the reversibility of an obstructed neuronal plasticity in Ts65Dn mice.
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Affiliation(s)
- Hanns Möhler
- Institute of Pharmacology, University of Zurich and, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.
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Adult-onset fluoxetine treatment does not improve behavioral impairments and may have adverse effects on the Ts65Dn mouse model of Down syndrome. Neural Plast 2012; 2012:467251. [PMID: 22848851 PMCID: PMC3405721 DOI: 10.1155/2012/467251] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Revised: 04/28/2012] [Accepted: 04/30/2012] [Indexed: 01/15/2023] Open
Abstract
Down syndrome is caused by triplication of chromosome 21 and is associated with neurocognitive phenotypes ranging from severe intellectual disability to various patterns of more selective neuropsychological deficits, including memory impairments. In the Ts65Dn mouse model of Down syndrome, excessive GABAergic neurotransmission results in local over-inhibition of hippocampal circuits, which dampens hippocampal synaptic plasticity and contributes to cognitive impairments. Treatments with several GABA(A) receptor antagonists result in increased plasticity and improved memory deficits in Ts65Dn mice. These GABA(A) receptor antagonists are, however, not suitable for clinical applications. The selective serotonin reuptake inhibitor fluoxetine, in contrast, is a widely prescribed antidepressant that can also enhance plasticity in the adult rodent brain by lowering GABAergic inhibition. For these reasons, we wondered if an adult-onset 4-week oral fluoxetine treatment restores spatial learning and memory impairments in Ts65Dn mice. Fluoxetine did not measurably improve behavioral impairments of Ts65Dn mice. On the contrary, we observed seizures and mortality in fluoxetine-treated Ts65Dn mice, raising the possibility of a drug × genotype interaction with respect to these adverse treatment outcomes. Future studies should re-address this in larger animal cohorts and determine if fluoxetine treatment is associated with adverse treatment effects in individuals with Down syndrome.
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Lack of behavioral and cognitive effects of chronic ethosuximide and gabapentin treatment in the Ts65Dn mouse model of Down syndrome. Neuroscience 2012; 220:158-68. [PMID: 22728103 DOI: 10.1016/j.neuroscience.2012.06.031] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2012] [Revised: 06/06/2012] [Accepted: 06/13/2012] [Indexed: 11/22/2022]
Abstract
The Ts65Dn (TS) mouse model of Down syndrome (DS) displays a number of behavioral, neuromorphological and neurochemical phenotypes of the syndrome. Altered GABAergic transmission appears to contribute to the mechanisms responsible for the cognitive impairments in TS mice. Increased functional expression of the trisomic gene encoding an inwardly rectifying potassium channel, subfamily J, member 6 (KCNJ6) has been reported in DS and TS mice, along with the consequent impairment in GAB Aergic function. Partial display of DS phenotypes in mice harboring a single trisomy of Kcnj6 provides compelling evidence for a functional role of increased channel expression in some of the abnormal neurological phenotypes found in DS. Notably, the antiepileptic drug (AED) ethosuximide (ETH), but not other AEDs such as gabapentin (GAB), is known to inhibit KCNJ6 channels in mice. Here, we report the effect of chronic ETH and GAB on the behavioral and cognitive phenotypes of TS and disomic control (CO) mice. Neither drug significantly affected sensorimotor abilities, motor coordination or spontaneous activity in TS and CO mice. Also, ETH and GAB did not induce anxiety in the open field or plus maze tests, did not alter performance in the Morris water maze, and did not affect cued - or context - fear conditioning. Our results thus suggest that KCNJ6 may not be a promising drug target candidate in DS. As a corollary, they also show that long-term use of ETH and GAB is devoid of adverse behavioral and cognitive effects.
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Mouse models of Down syndrome as a tool to unravel the causes of mental disabilities. Neural Plast 2012; 2012:584071. [PMID: 22685678 PMCID: PMC3364589 DOI: 10.1155/2012/584071] [Citation(s) in RCA: 128] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Revised: 03/23/2012] [Accepted: 03/24/2012] [Indexed: 12/16/2022] Open
Abstract
Down syndrome (DS) is the most common genetic cause of mental disability. Based on the homology of Hsa21 and the murine chromosomes Mmu16, Mmu17 and Mmu10, several mouse models of DS have been developed. The most commonly used model, the Ts65Dn mouse, has been widely used to investigate the neural mechanisms underlying the mental disabilities seen in DS individuals. A wide array of neuromorphological alterations appears to compromise cognitive performance in trisomic mice. Enhanced inhibition due to alterations in GABA(A)-mediated transmission and disturbances in the glutamatergic, noradrenergic and cholinergic systems, among others, has also been demonstrated. DS cognitive dysfunction caused by neurodevelopmental alterations is worsened in later life stages by neurodegenerative processes. A number of pharmacological therapies have been shown to partially restore morphological anomalies concomitantly with cognition in these mice. In conclusion, the use of mouse models is enormously effective in the study of the neurobiological substrates of mental disabilities in DS and in the testing of therapies that rescue these alterations. These studies provide the basis for developing clinical trials in DS individuals and sustain the hope that some of these drugs will be useful in rescuing mental disabilities in DS individuals.
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Buga AM, Vintilescu R, Balseanu AT, Pop OT, Streba C, Toescu E, Popa-Wagner A. Repeated PTZ treatment at 25-day intervals leads to a highly efficient accumulation of doublecortin in the dorsal hippocampus of rats. PLoS One 2012; 7:e39302. [PMID: 22768071 PMCID: PMC3387140 DOI: 10.1371/journal.pone.0039302] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Accepted: 05/23/2012] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND Neurogenesis persists throughout life in the adult mammalian brain. Because neurogenesis can only be assessed in postmortem tissue, its functional significance remains undetermined, and identifying an in vivo correlate of neurogenesis has become an important goal. By studying pentylenetetrazole-induced brain stimulation in a rat model of kindling we accidentally discovered that 25±1 days periodic stimulation of Sprague-Dawley rats led to a highly efficient increase in seizure susceptibility. METHODOLOGY/PRINCIPAL FINDINGS By EEG, RT-PCR, western blotting and immunohistochemistry, we show that repeated convulsive seizures with a periodicity of 25±1 days led to an enrichment of newly generated neurons, that were BrdU-positive in the dentate gyrus at day 25±1 post-seizure. At the same time, there was a massive increase in the number of neurons expressing the migratory marker, doublecortin, at the boundary between the granule cell layer and the polymorphic layer in the dorsal hippocampus. Some of these migrating neurons were also positive for NeuN, a marker for adult neurons. CONCLUSION/SIGNIFICANCE Our results suggest that the increased susceptibility to seizure at day 25±1 post-treatment is coincident with a critical time required for newborn neurons to differentiate and integrate into the existing hippocampal network, and outlines the importance of the dorsal hippocampus for seizure-related neurogenesis. This model can be used as an in vivo correlate of neurogenesis to study basic questions related to neurogenesis and to the neurogenic mechanisms that contribute to the development of epilepsy.
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Affiliation(s)
- Ana-Maria Buga
- Department of Psychiatry, Molecular Psychiatry, Rostock University Medical School, Rostock, Germany
- Department of Functional Sciences, University of Medicine and Pharmacy, Craiova, Romania
| | - Raluca Vintilescu
- Department of Functional Sciences, University of Medicine and Pharmacy, Craiova, Romania
| | - Adrian Tudor Balseanu
- Department of Psychiatry, Molecular Psychiatry, Rostock University Medical School, Rostock, Germany
- Department of Functional Sciences, University of Medicine and Pharmacy, Craiova, Romania
| | - Oltin Tiberiu Pop
- Department of Functional Sciences, University of Medicine and Pharmacy, Craiova, Romania
| | - Costin Streba
- Department of Functional Sciences, University of Medicine and Pharmacy, Craiova, Romania
| | - Emil Toescu
- Department of Clinical and Experimental Medicine, College of Medical and Dental Sciences University of Birmingham Edgbaston, Birmingham, United Kingdom
| | - Aurel Popa-Wagner
- Department of Psychiatry, Molecular Psychiatry, Rostock University Medical School, Rostock, Germany
- Department of Functional Sciences, University of Medicine and Pharmacy, Craiova, Romania
- * E-mail:
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59
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Currier DG, Polk RC, Reeves RH. A Sonic hedgehog (Shh) response deficit in trisomic cells may be a common denominator for multiple features of Down syndrome. PROGRESS IN BRAIN RESEARCH 2012; 197:223-36. [PMID: 22541295 PMCID: PMC4405118 DOI: 10.1016/b978-0-444-54299-1.00011-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The hedgehog (HH) family of growth factors is involved in many aspects of growth and development, from the establishment of left-right axes at gastrulation to the patterning and formation of multiple structures in essentially every tissue, to the maintenance and regulation of stem cell populations in adults. Sonic hedgehog (Shh) in particular acts as a mitogen, regulating proliferation of target cells, a growth factor that triggers differentiation in target populations, and a morphogen causing cells to respond differently based on their positions along a spatial and temporal concentration gradient. Given its very broad range of effects in development, it is not surprising that many of the structures affected by a disruption in Shh signaling are also affected in Down syndrome (DS). However, recent studies have shown that trisomic cerebellar granule cell precursors have a deficit, compared to their euploid counterparts, in their response to the mitogenic effects of Shh. This deficit substantially contributes to the hypocellular cerebellum in mouse models that parallels the human DS phenotype and can be corrected in early development by a single exposure to a small-molecule agonist of the Shh pathway. Here, we consider how an attenuated Shh response might affect several aspects of development to produce multiple phenotypic outcomes observed in DS.
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Affiliation(s)
- Duane G. Currier
- Department of Physiology and The McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Renita C. Polk
- Department of Physiology and The McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Roger H. Reeves
- Department of Physiology and The McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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Kleschevnikov AM, Belichenko PV, Salehi A, Wu C. Discoveries in Down syndrome: moving basic science to clinical care. PROGRESS IN BRAIN RESEARCH 2012; 197:199-221. [PMID: 22541294 DOI: 10.1016/b978-0-444-54299-1.00010-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
This review describes recent discoveries in neurobiology of Down syndrome (DS) achieved with use of mouse genetic models and provides an overview of experimental approaches aimed at development of pharmacological restoration of cognitive function in people with this developmental disorder. Changes in structure and function of synaptic connections within the hippocampal formation of DS model mice, as well as alterations in innervations of the hippocampus by noradrenergic and cholinergic neuromodulatory systems, provided important clues for potential pharmacological treatments of cognitive disabilities in DS. Possible molecular and cellular mechanisms underlying this genetic disorder have been addressed. We discuss novel mechanisms engaging misprocessing of amyloid precursor protein (App) and other proteins, through their affect on axonal transport and endosomal dysfunction, to "Alzheimer-type" neurodegenerative processes that affect cognition later in life. In conclusion, a number of therapeutic strategies have been defined that may restore cognitive function in mouse models of DS. In the juvenile and young animals, these strategists focus on restoration of synaptic plasticity, rate of adult neurogenesis, and functions of the neuromodulatory subcortical systems. Later in life, the major focus is on recuperation of misprocessed App and related proteins. It is hoped that the identification of an increasing number of potential targets for pharmacotherapy of cognitive deficits in DS will add to the momentum for creating and completing clinical trials.
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Affiliation(s)
- A M Kleschevnikov
- Department of Neurosciences, University of California, San Diego, La Jolla, CA, USA.
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61
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Hagerman R, Lauterborn J, Au J, Berry-Kravis E. Fragile X syndrome and targeted treatment trials. Results Probl Cell Differ 2012; 54:297-335. [PMID: 22009360 PMCID: PMC4114775 DOI: 10.1007/978-3-642-21649-7_17] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Work in recent years has revealed an abundance of possible new treatment targets for fragile X syndrome (FXS). The use of animal models, including the fragile X knockout mouse which manifests a phenotype very similar to FXS in humans, has resulted in great strides in this direction of research. The lack of Fragile X Mental Retardation Protein (FMRP) in FXS causes dysregulation and usually overexpression of a number of its target genes, which can cause imbalances of neurotransmission and deficits in synaptic plasticity. The use of metabotropic glutamate receptor (mGluR) blockers and gamma amino-butyric acid (GABA) agonists have been shown to be efficacious in reversing cellular and behavioral phenotypes, and restoring proper brain connectivity in the mouse and fly models. Proposed new pharmacological treatments and educational interventions are discussed in this chapter. In combination, these various targeted treatments show promising preliminary results in mitigating or even reversing the neurobiological abnormalities caused by loss of FMRP, with possible translational applications to other neurodevelopmental disorders including autism.
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Affiliation(s)
- Randi Hagerman
- Department of Pediatrics, University of California, Sacramento, CA, USA.
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62
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Garner CC, Wetmore DZ. Synaptic Pathology of Down Syndrome. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 970:451-68. [DOI: 10.1007/978-3-7091-0932-8_20] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Begenisic T, Spolidoro M, Braschi C, Baroncelli L, Milanese M, Pietra G, Fabbri ME, Bonanno G, Cioni G, Maffei L, Sale A. Environmental enrichment decreases GABAergic inhibition and improves cognitive abilities, synaptic plasticity, and visual functions in a mouse model of Down syndrome. Front Cell Neurosci 2011; 5:29. [PMID: 22207837 PMCID: PMC3245647 DOI: 10.3389/fncel.2011.00029] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Accepted: 12/12/2011] [Indexed: 01/20/2023] Open
Abstract
Down syndrome (DS) is the most common genetic disorder associated with mental retardation. It has been repeatedly shown that Ts65Dn mice, the prime animal model for DS, have severe cognitive and neural plasticity defects due to excessive inhibition. We report that increasing sensory-motor stimulation in adulthood through environmental enrichment (EE) reduces brain inhibition levels and promotes recovery of spatial memory abilities, hippocampal synaptic plasticity, and visual functions in adult Ts65Dn mice.
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64
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Weng SM, Bailey MES, Cobb SR. Rett syndrome: from bed to bench. Pediatr Neonatol 2011; 52:309-16. [PMID: 22192257 DOI: 10.1016/j.pedneo.2011.08.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Revised: 03/30/2011] [Accepted: 04/22/2011] [Indexed: 02/05/2023] Open
Abstract
Rett syndrome (RTT), a neurodevelopmental condition characterized by delayed-onset loss of spoken language and the development of distinctive hand stereotypies, affects approximately 1 in 10,000 live female births. Clinical diagnosis has been based on symptoms such as loss of acquired purposeful hand skills, autistic behaviors, motor dysfunctions, seizure disorders, and gait abnormalities. RTT is a genetic disease and is caused almost exclusively by mutations in the X-linked gene, MECP2, to produce a phenotype that is thought to be primarily of neurological origin. Clinical reports show RTT patients to have a smaller brain volume, especially in the cerebral hemispheres, and alterations in various neurotransmitter systems, including acetylcholine, dopamine, serotonin, glutamate, substance P, and various trophic factors. Because of its monogenetic characteristic, disruption of Mecp2 is readily recapitulated in mice to produce a prominent RTT-like phenotype and provide an excellent platform for understanding the pathogenesis of RTT. As shown in human studies, Mecp2 mutants also display subtle alterations in neuronal morphology, including smaller cortical neurons with a higher-packing density and reduced dendritic complexity. Neurophysiological studies in Mecp2-mutant mice consistently report alterations in synaptic function, notably, defects in synaptic plasticity. These data suggest that RTT might be regarded as a synaptopathy (disease of the synapse) and thus potentially amenable to rational therapeutic intervention.
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Affiliation(s)
- Shih-Ming Weng
- Institute for Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom
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Brault V, Martin B, Costet N, Bizot JC, Hérault Y. Characterization of PTZ-induced seizure susceptibility in a down syndrome mouse model that overexpresses CSTB. PLoS One 2011; 6:e27845. [PMID: 22140471 PMCID: PMC3227573 DOI: 10.1371/journal.pone.0027845] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Accepted: 10/26/2011] [Indexed: 12/27/2022] Open
Abstract
Down syndrome (DS) is a complex genetic syndrome characterized by intellectual disability, dysmorphism and variable additional physiological traits. Current research progress has begun to decipher the neural mechanisms underlying cognitive impairment, leading to new therapeutic perspectives. Pentylenetetrazol (PTZ) has recently been found to have positive effects on learning and memory capacities of a DS mouse model and is foreseen to treat DS patients. But PTZ is also known to be a convulsant drug at higher dose and DS persons are more prone to epileptic seizures than the general population. This raises concerns over what long-term effects of treatment might be in the DS population. The cause of increased propensity for epilepsy in the DS population and which Hsa21 gene(s) are implicated remain unknown. Among Hsa21 candidate genes in epilepsy, CSTB, coding for the cystein protease inhibitor cystatin B, is involved in progressive myoclonus epilepsy and ataxia in both mice and human. Thus we aim to evaluate the effect of an increase in Cstb gene dosage on spontaneous epileptic activity and susceptibility to PTZ-induced seizure. To this end we generated a new mouse model trisomic for Cstb by homologous recombination. We verified that increasing copy number of Cstb from Trisomy (Ts) to Tetrasomy (Tt) was driving overexpression of the gene in the brain, we checked transgenic animals for presence of locomotor activity and electroencephalogram (EEG) abnormalities characteristic of myoclonic epilepsy and we tested if those animals were prone to PTZ-induced seizure. Overall, the results of the analysis shows that an increase in Cstb does not induce any spontaneous epileptic activity and neither increase or decrease the propensity of Ts and Tt mice to myoclonic seizures suggesting that Ctsb dosage should not interfere with PTZ-treatment.
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Affiliation(s)
- Véronique Brault
- Department of Translational Medicine and Neurogenetics, Institut de Génétique Biologie Moléculaire et Cellulaire (IGBMC), Inserm U596, CNRS UMR7104, Université de Strasbourg, Illkirch, France
| | - Benoît Martin
- Inserm U642, Rennes, France
- Laboratoire Traitement du Signal et de l'Image, Université de Rennes 1, Rennes, France
| | - Nathalie Costet
- Inserm U642, Rennes, France
- Laboratoire Traitement du Signal et de l'Image, Université de Rennes 1, Rennes, France
| | | | - Yann Hérault
- Department of Translational Medicine and Neurogenetics, Institut de Génétique Biologie Moléculaire et Cellulaire (IGBMC), Inserm U596, CNRS UMR7104, Université de Strasbourg, Illkirch, France
- Transgenese et Archivage Animaux Modèles, TAAM, CNRS, UPS44, Orléans, France
- Institut Français Clinique de la Souris, GIE CERBM, Illkirch, France
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Abstract
Mutations in the X-linked gene MECP2 (methyl CpG-binding protein 2) are the primary cause of the neurodevelopmental disorder RTT (Rett syndrome), and are also implicated in other neurological conditions. The expression product of this gene, MeCP2, is a widely expressed nuclear protein, especially abundant in mature neurons of the CNS (central nervous system). The major recognized consequences of MECP2 mutation occur in the CNS, but there is growing awareness of peripheral effects contributing to the full RTT phenotype. MeCP2 is classically considered to act as a DNA methylation-dependent transcriptional repressor, but may have additional roles in regulating gene expression and chromatin structure. Knocking out Mecp2 function in mice recapitulates many of the overt neurological features seen in RTT patients, and the characteristic postnatally delayed onset of symptoms is accompanied by aberrant neuronal morphology and deficits in synaptic physiology. Evidence that reactivation of endogenous Mecp2 in mutant mice, even at adult stages, can reverse aspects of RTT-like pathology and result in apparently functionally mature neurons has provided renewed hope for patients, but has also provoked discussion about traditional boundaries between neurodevelopmental disorders and those involving dysfunction at later stages. In the present paper we review the neurobiology of MeCP2 and consider the various genetic (including gene therapy), pharmacological and environmental interventions that have been, and could be, developed to attempt phenotypic rescue in RTT. Such approaches are already providing valuable insights into the potential tractability of RTT and related conditions, and are useful pointers for the development of future therapeutic strategies.
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67
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Simoes de Souza FM, Busquet N, Blatner M, Maclean KN, Restrepo D. Galantamine improves olfactory learning in the Ts65Dn mouse model of Down syndrome. Sci Rep 2011; 1:137. [PMID: 22355654 PMCID: PMC3216618 DOI: 10.1038/srep00137] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Accepted: 09/28/2011] [Indexed: 11/20/2022] Open
Abstract
Down syndrome (DS) is the most common form of congenital intellectual disability. Although DS involves multiple disturbances in various tissues, there is little doubt that in terms of quality of life cognitive impairment is the most serious facet and there is no effective treatment for this aspect of the syndrome. The Ts65Dn mouse model of DS recapitulates multiple aspects of DS including cognitive impairment. Here the Ts65Dn mouse model of DS was evaluated in an associative learning paradigm based on olfactory cues. In contrast to disomic controls, trisomic mice exhibited significant deficits in olfactory learning. Treatment of trisomic mice with the acetylcholinesterase inhibitor galantamine resulted in a significant improvement in olfactory learning. Collectively, our study indicates that olfactory learning can be a sensitive tool for evaluating deficits in associative learning in mouse models of DS and that galantamine has therapeutic potential for improving cognitive abilities.
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Affiliation(s)
- Fabio M. Simoes de Souza
- Cell and Developmental Biology, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, U.S.A.
- These authors contributed equally to this work
| | - Nicolas Busquet
- Cell and Developmental Biology, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, U.S.A.
- Department of Pediatrics, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, U.S.A
- These authors contributed equally to this work
| | | | - Kenneth N. Maclean
- Department of Pediatrics, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, U.S.A
| | - Diego Restrepo
- Cell and Developmental Biology, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, U.S.A.
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Chronic Treatment with a Promnesiant GABA-A α5-Selective Inverse Agonist Increases Immediate Early Genes Expression during Memory Processing in Mice and Rectifies Their Expression Levels in a Down Syndrome Mouse Model. Adv Pharmacol Sci 2011; 2011:153218. [PMID: 22028705 PMCID: PMC3199058 DOI: 10.1155/2011/153218] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Revised: 07/27/2011] [Accepted: 07/31/2011] [Indexed: 12/20/2022] Open
Abstract
Decrease of GABAergic transmission has been proposed to improve memory functions. Indeed, inverse agonists selective for α5 GABA-A-benzodiazepine receptors (α5IA) have promnesiant activity. Interestingly, we have recently shown that α5IA can rescue cognitive deficits in Ts65Dn mice, a Down syndrome mouse model with altered GABAergic transmission. Here, we studied the impact of chronic treatment with α5IA on gene expression in the hippocampus of Ts65Dn and control euploid mice after being trained in the Morris water maze task. In euploid mice, chronic treatment with α5IA increased IEGs expression, particularly of c-Fos and Arc genes. In Ts65Dn mice, deficits of IEGs activation were completely rescued after treatment with α5IA. In addition, normalization of Sod1 overexpression in Ts65Dn mice after α5IA treatment was observed. IEG expression regulation after α5IA treatment following behavioral stimulation could be a contributing factor for both the general promnesiant activity of α5IA and its rescuing effect in Ts65Dn mice alongside signaling cascades that are critical for memory consolidation and cognition.
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69
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Kleschevnikov AM, Belichenko PV, Gall J, George L, Nosheny R, Maloney MT, Salehi A, Mobley WC. Increased efficiency of the GABAA and GABAB receptor-mediated neurotransmission in the Ts65Dn mouse model of Down syndrome. Neurobiol Dis 2011; 45:683-91. [PMID: 22062771 DOI: 10.1016/j.nbd.2011.10.009] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Revised: 09/14/2011] [Accepted: 10/08/2011] [Indexed: 01/06/2023] Open
Abstract
Cognitive impairment in Down syndrome (DS) involves the hippocampus. In the Ts65Dn mouse model of DS, deficits in hippocampus-dependent learning and synaptic plasticity were linked to enhanced inhibition. However, the mechanistic basis of changes in inhibitory efficiency remains largely unexplored, and efficiency of the GABAergic synaptic neurotransmission has not yet been investigated in direct electrophysiological experiments. To investigate this important feature of neurobiology of DS, we examined synaptic and molecular properties of the GABAergic system in the dentate gyrus (DG) of adult Ts65Dn mice. Both GABAA and GABAB receptor-mediated components of evoked inhibitory postsynaptic currents (IPSCs) were significantly increased in Ts65Dn vs. control (2N) DG granule cells. These changes were unaccompanied by alterations in hippocampal levels of GABAA (α1, α2, α3, α5 and γ2) or GABAB (Gbr1a and Gbr1b) receptor subunits. Immunoreactivity for GAD65, a marker for GABAergic terminals, was also unchanged. In contrast, there was a marked change in functional parameters of GABAergic synapses. Paired stimulations showed reduced paired-pulse ratios of both GABAA and GABAB receptor-mediated IPSC components (IPSC2/IPSC1), suggesting an increase in presynaptic release of GABA. Consistent with increased gene dose, the level of the Kir3.2 subunit of potassium channels, effectors for postsynaptic GABAB receptors, was increased. This change was associated with enhanced postsynaptic GABAB/Kir3.2 signaling following application of the GABAB receptor agonist baclofen. Thus, both GABAA and GABAB receptor-mediated synaptic efficiency is increased in the Ts65Dn DG, thus likely contributing to deficient synaptic plasticity and poor learning in DS.
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Affiliation(s)
- Alexander M Kleschevnikov
- Department of Neurosciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
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70
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Duchon A, Raveau M, Chevalier C, Nalesso V, Sharp AJ, Herault Y. Identification of the translocation breakpoints in the Ts65Dn and Ts1Cje mouse lines: relevance for modeling Down syndrome. Mamm Genome 2011; 22:674-84. [PMID: 21953411 PMCID: PMC3224224 DOI: 10.1007/s00335-011-9356-0] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Accepted: 09/05/2011] [Indexed: 12/16/2022]
Abstract
Down syndrome (DS) is the most frequent genetic disorder leading to intellectual disabilities and is caused by three copies of human chromosome 21. Mouse models are widely used to better understand the physiopathology in DS or to test new therapeutic approaches. The older and the most widely used mouse models are the trisomic Ts65Dn and the Ts1Cje mice. They display deficits similar to those observed in DS people, such as those in behavior and cognition or in neuronal abnormalities. The Ts65Dn model is currently used for further therapeutic assessment of candidate drugs. In both models, the trisomy was induced by reciprocal chromosomal translocations that were not further characterized. Using a comparative genomic approach, we have been able to locate precisely the translocation breakpoint in these two models and we took advantage of this finding to derive a new and more efficient Ts65Dn genotyping strategy. Furthermore, we found that the translocations introduce additional aneuploidy in both models, with a monosomy of seven genes in the most telomeric part of mouse chromosome 12 in the Ts1Cje and a trisomy of 60 centromeric genes on mouse chromosome 17 in the Ts65Dn. Finally, we report here the overexpression of the newly found aneuploid genes in the Ts65Dn heart and we discuss their potential impact on the validity of the DS model.
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Affiliation(s)
- Arnaud Duchon
- Institut de Génétique Biologie Moléculaire et Cellulaire, Translational Medicine and Neuroscience Program, Université de Strasbourg, Illkirch, France
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71
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Costa ACS. On the promise of pharmacotherapies targeted at cognitive and neurodegenerative components of Down syndrome. Dev Neurosci 2011; 33:414-27. [PMID: 21893967 PMCID: PMC3254040 DOI: 10.1159/000330861] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Accepted: 07/14/2011] [Indexed: 01/08/2023] Open
Abstract
Down syndrome (DS) is the phenotypic consequence of trisomy 21 and is the most common genetically defined cause of intellectual disability. The most complete, widely available, and well-studied animal model of DS is the Ts65Dn mouse. Recent preclinical successes in rescuing learning and memory deficits in Ts65Dn mice are legitimate causes for optimism that pharmacotherapies for cognitive deficits in DS might be within reach. This article provides a snapshot of potential pharmacotherapies for DS, with emphasis on our recent results showing that the N-methyl-D-aspartate receptor antagonist memantine can reverse learning and memory deficits in Ts65Dn mice. Because memantine has already been approved for the therapy of Alzheimer's dementia, we have been able to very rapidly translate these results into human research and are currently conducting a 16-week, randomized, double-blind, placebo-controlled evaluation of the efficacy, tolerability and safety of memantine hydrochloride on enhancing the cognitive abilities of young adults with DS. The design and current status of this clinical trial will be discussed, which will be followed by some speculation on the potential impact of this and future clinical trials in the field of DS.
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Affiliation(s)
- Alberto C S Costa
- Division of Clinical Pharmacology and Toxicology, Department of Medicine, University of Colorado Denver Anschutz Medical Campus, Aurora, CO 80045, USA.
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72
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Das I, Reeves RH. The use of mouse models to understand and improve cognitive deficits in Down syndrome. Dis Model Mech 2011; 4:596-606. [PMID: 21816951 PMCID: PMC3180223 DOI: 10.1242/dmm.007716] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Remarkable advances have been made in recent years towards therapeutics for cognitive impairment in individuals with Down syndrome (DS) by using mouse models. In this review, we briefly describe the phenotypes of mouse models that represent outcome targets for drug testing, the behavioral tests used to assess impairments in cognition and the known mechanisms of action of several drugs that are being used in preclinical studies or are likely to be tested in clinical trials. Overlaps in the distribution of targets and in the pathways that are affected by these diverse drugs in the trisomic brain suggest new avenues for DS research and drug development.
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Affiliation(s)
- Ishita Das
- Department of Physiology and McKusick-Nathans, Institute for Medical Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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73
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Braudeau J, Delatour B, Duchon A, Pereira PL, Dauphinot L, de Chaumont F, Olivo-Marin JC, Dodd RH, Hérault Y, Potier MC. Specific targeting of the GABA-A receptor α5 subtype by a selective inverse agonist restores cognitive deficits in Down syndrome mice. J Psychopharmacol 2011; 25:1030-42. [PMID: 21693554 PMCID: PMC3160204 DOI: 10.1177/0269881111405366] [Citation(s) in RCA: 121] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
An imbalance between inhibitory and excitatory neurotransmission has been proposed to contribute to altered brain function in individuals with Down syndrome (DS). Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system and accordingly treatment with GABA-A antagonists can efficiently restore cognitive functions of Ts65Dn mice, a genetic model for DS. However, GABA-A antagonists are also convulsant which preclude their use for therapeutic intervention in DS individuals. Here, we have evaluated safer strategies to release GABAergic inhibition using a GABA-A-benzodiazepine receptor inverse agonist selective for the α5-subtype (α5IA). We demonstrate that α5IA restores learning and memory functions of Ts65Dn mice in the novel-object recognition and in the Morris water maze tasks. Furthermore, we show that following behavioural stimulation, α5IA enhances learning-evoked immediate early gene products in specific brain regions involved in cognition. Importantly, acute and chronic treatments with α5IA do not induce any convulsant or anxiogenic effects that are associated with GABA-A antagonists or non-selective inverse agonists of the GABA-A-benzodiazepine receptors. Finally, chronic treatment with α5IA did not induce histological alterations in the brain, liver and kidney of mice. Our results suggest that non-convulsant α5-selective GABA-A inverse agonists could improve learning and memory deficits in DS individuals.
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Affiliation(s)
- J Braudeau
- Centre de Recherche de l'Institut du
Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM UMRS 975, UPMC, Paris,
France.,CNRS, Lab NAMC, UMR8620, Université
Paris Sud, Orsay, France
| | - B Delatour
- Centre de Recherche de l'Institut du
Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM UMRS 975, UPMC, Paris,
France.,CNRS, Lab NAMC, UMR8620, Université
Paris Sud, Orsay, France
| | - A Duchon
- Institut de Génétique et de Biologie
Moléculaire et Cellulaire (IGBMC), Institut National de Santé et de Recherche
Médicale (INSERM) U964/Centre National de Recherche Scientifique (CNRS) UMR
1704/Université de Strasbourg, 67404 Illkirch, France.,Institut Clinique de la Souris (ICS),
Groupe d'Intérêt Economique Centre Européen de Recherche en Biologie et en Médecine
(GIE-CERBM), INSERM, CNRS, Université de Strasbourg, Illkirch, France
| | - P Lopes Pereira
- Institut de Génétique et de Biologie
Moléculaire et Cellulaire (IGBMC), Institut National de Santé et de Recherche
Médicale (INSERM) U964/Centre National de Recherche Scientifique (CNRS) UMR
1704/Université de Strasbourg, 67404 Illkirch, France
| | - L Dauphinot
- Centre de Recherche de l'Institut du
Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM UMRS 975, UPMC, Paris,
France
| | - F de Chaumont
- Institut Pasteur, Quantitative Image
Analysis Unit, CNRS URA 2582, 75015 Paris, France
| | - J-C Olivo-Marin
- Institut Pasteur, Quantitative Image
Analysis Unit, CNRS URA 2582, 75015 Paris, France
| | - RH Dodd
- Institut de Chimie des Substances
Naturelles - CNRS UPR 2301, Gif-sur-Yvette, France
| | - Y Hérault
- Institut de Génétique et de Biologie
Moléculaire et Cellulaire (IGBMC), Institut National de Santé et de Recherche
Médicale (INSERM) U964/Centre National de Recherche Scientifique (CNRS) UMR
1704/Université de Strasbourg, 67404 Illkirch, France.,Institut Clinique de la Souris (ICS),
Groupe d'Intérêt Economique Centre Européen de Recherche en Biologie et en Médecine
(GIE-CERBM), INSERM, CNRS, Université de Strasbourg, Illkirch, France
| | - M-C Potier
- Centre de Recherche de l'Institut du
Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM UMRS 975, UPMC, Paris,
France.,M-C Potier, Centre de Recherche de
l'Institut du Cerveau et de Moelle Epinière, CNRS UMR7225, INSERM UMRS 975,
UPMC, 75013 Paris, France
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74
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Ramamoorthi K, Lin Y. The contribution of GABAergic dysfunction to neurodevelopmental disorders. Trends Mol Med 2011; 17:452-62. [PMID: 21514225 DOI: 10.1016/j.molmed.2011.03.003] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2011] [Revised: 03/04/2011] [Accepted: 03/10/2011] [Indexed: 12/31/2022]
Abstract
GABA (γ-aminobutyric acid) is the major inhibitory neurotransmitter in the brain. The GABAergic system is indispensable for maintaining the balance between excitation and inhibition (E/I balance) required for normal neural circuit function. E/I imbalances that result from perturbations in the development of this system, ranging from the generation of inhibitory neurons to the formation of their synaptic connections, have been implicated in several neurodevelopmental disorders. In this review, we discuss how impairments at different stages in GABAergic development can lead to disease states. We also highlight recent studies which show that modulation of the GABAergic system can successfully reverse cognitive deficits in disease models and suggest that therapeutic strategies targeting the GABAergic system could be effective in treating neurodevelopmental disorders.
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Affiliation(s)
- Kartik Ramamoorthi
- McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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75
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Nelson ED, Bal M, Kavalali ET, Monteggia LM. Selective impact of MeCP2 and associated histone deacetylases on the dynamics of evoked excitatory neurotransmission. J Neurophysiol 2011; 106:193-201. [PMID: 21511710 DOI: 10.1152/jn.00751.2010] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
An imbalance between the strengths of excitatory and inhibitory synaptic inputs has been proposed as the cellular basis of autism and related neurodevelopmental disorders. Previous studies examining spontaneous levels of excitatory and inhibitory neurotransmission in the forebrain regions of methyl-CpG-binding protein 2 (Mecp2) mutant mice, models of the autism spectrum disorder Rett syndrome, have identified a decrease in excitatory drive, in some cases coupled with an increase in inhibitory synaptic strength, as a major source of this imbalance. Here, we reevaluated this question by examining the short-term dynamics of evoked neurotransmission between hippocampal neurons cultured from MeCP2 knockout mice and found a marked increase in evoked excitatory neurotransmission that is consistent with an increase in presynaptic release probability. This increase in evoked excitatory drive was not matched with alterations in evoked inhibitory neurotransmission. Moreover, we observed similar excitatory drive specific changes after the loss of key histone deacetylases (histone deacetylase 1 and 2) that form a complex with MeCP2 and mediate transcriptional regulation. These findings suggest a distinct role for MeCP2 and its cofactors in the regulation of evoked excitatory neurotransmission compared with their essential role in basal synaptic activity.
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Affiliation(s)
- Erika D Nelson
- Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9070, USA
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76
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Wallace TL, Ballard TM, Pouzet B, Riedel WJ, Wettstein JG. Drug targets for cognitive enhancement in neuropsychiatric disorders. Pharmacol Biochem Behav 2011; 99:130-45. [PMID: 21463652 DOI: 10.1016/j.pbb.2011.03.022] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 03/18/2011] [Accepted: 03/28/2011] [Indexed: 12/11/2022]
Abstract
The investigation of novel drug targets for treating cognitive impairments associated with neurological and psychiatric disorders remains a primary focus of study in central nervous system (CNS) research. Many promising new therapies are progressing through preclinical and clinical development, and offer the potential of improved treatment options for neurodegenerative diseases such as Alzheimer's disease (AD) as well as other disorders that have not been particularly well treated to date like the cognitive impairments associated with schizophrenia (CIAS). Among targets under investigation, cholinergic receptors have received much attention with several nicotinic agonists (α7 and α4β2) actively in clinical trials for the treatment of AD, CIAS and attention deficit hyperactivity disorder (ADHD). Both glutamatergic and serotonergic (5-HT) agonists and antagonists have profound effects on neurotransmission and improve cognitive function in preclinical experiments with animals; some of these compounds are now in proof-of-concept studies in humans. Several histamine H3 receptor antagonists are in clinical development not only for cognitive enhancement, but also for the treatment of narcolepsy and cognitive deficits due to sleep deprivation because of their expression in brain sleep centers. Compounds that dampen inhibitory tone (e.g., GABA(A) α5 inverse agonists) or elevate excitatory tone (e.g., glycine transporter inhibitors) offer novel approaches for treating diseases such as schizophrenia, AD and Down syndrome. In addition to cell surface receptors, intracellular drug targets such as the phosphodiesterases (PDEs) are known to impact signaling pathways that affect long-term memory formation and working memory. Overall, there is a genuine need to treat cognitive deficits associated with many neuropsychiatric conditions as well as an increasingly aging population.
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MESH Headings
- Animals
- Cognition Disorders/drug therapy
- Cognition Disorders/physiopathology
- Glycine Plasma Membrane Transport Proteins/drug effects
- Glycine Plasma Membrane Transport Proteins/physiology
- Humans
- Learning/drug effects
- Learning/physiology
- Memory/drug effects
- Memory/physiology
- Nootropic Agents/pharmacology
- Phosphodiesterase Inhibitors/pharmacology
- Receptors, Cholinergic/drug effects
- Receptors, Cholinergic/physiology
- Receptors, Dopamine/drug effects
- Receptors, Dopamine/physiology
- Receptors, GABA/drug effects
- Receptors, GABA/physiology
- Receptors, Glutamate/drug effects
- Receptors, Glutamate/physiology
- Receptors, Histamine/drug effects
- Receptors, Histamine/physiology
- Receptors, Serotonin/drug effects
- Receptors, Serotonin/physiology
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Affiliation(s)
- Tanya L Wallace
- Center for Neuroscience, SRI International, Menlo Park, CA, USA
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77
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Calfa G, Percy AK, Pozzo-Miller L. Experimental models of Rett syndrome based on Mecp2 dysfunction. Exp Biol Med (Maywood) 2011; 236:3-19. [PMID: 21239731 DOI: 10.1258/ebm.2010.010261] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Rett syndrome (RTT) is a neurodevelopmental disorder predominantly occurring in females with an incidence of 1:10,000 births and caused by sporadic mutations in the MECP2 gene, which encodes methyl-CpG-binding protein-2, an epigenetic transcription factor that binds methylated DNA. The clinical hallmarks include a period of apparently normal early development followed by a plateau and then subsequent frank regression. Impaired visual and aural contact often lead to an initial diagnosis of autism. The characterization of experimental models based on the loss-of-function of the mouse Mecp2 gene revealed that subtle changes in the morphology and function of brain cells and synapses have profound consequences on network activities that underlie critical brain functions. Furthermore, these experimental models have been used for successful reversals of RTT-like symptoms by genetic, pharmacological and environmental manipulations, raising hope for novel therapeutic strategies to improve the quality of life of RTT individuals.
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Affiliation(s)
- Gaston Calfa
- Department of Neurobiology, The University of Alabama at Birmingham, Birmingham, AL 35294, USA
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78
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Sharma A. Transcriptome bioinformatic analysis identifies potential therapeutic mechanism of pentylenetetrazole in down syndrome. BioData Min 2010; 3:7. [PMID: 21029440 PMCID: PMC2987760 DOI: 10.1186/1756-0381-3-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Accepted: 10/28/2010] [Indexed: 11/29/2022] Open
Abstract
Background Pentylenetetrazole (PTZ) has recently been found to ameliorate cognitive impairment in rodent models of Down syndrome (DS). The mechanism underlying PTZ's therapeutic effect in DS is however not clear. Microarray profiling has previously reported differential expression, both up- and down-regulation, of genes in DS. Given this, transcriptomic data related to PTZ treatment, if available, could be used to understand the drug's therapeutic mechanism in DS. No such mammalian data however exists. Nevertheless, a Drosophila model inspired by PTZ induced kindling plasticity in rodents has recently been described. Microarray profiling has shown PTZ's downregulatory effect on gene expression in the fly heads. Methods In a comparative transcriptomics approach, I have analyzed the available microarray data in order to identify potential therapeutic mechanism of PTZ in DS. In the analysis, summary data of up- and down-regulated genes reported in human DS studies and of down-regulated genes reported in the Drosophila model has been used. Results I find that transcriptomic correlate of chronic PTZ in Drosophila counteracts that of DS. Genes downregulated by PTZ significantly over-represent genes upregulated in DS and under-represent genes downregulated in DS. Further, the genes which are common in the downregulated and upregulated DS set show enrichment for MAP kinase pathway. Conclusion My analysis suggests that downregulation of MAP kinase pathway may mediate therapeutic effect of PTZ in DS. Existing evidence implicating MAP kinase pathway in DS supports this observation.
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Affiliation(s)
- Abhay Sharma
- Institute of Genomics and Integrative Biology, Council of Scientific and Industrial Research Delhi University Campus, Mall Road, Delhi 110007, India.
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79
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Abstract
A growing and interdisciplinary translational neuroscience research effort for neurodevelopmental disorders (NDDs) is investigating the mechanisms of dysfunction and testing effective treatment strategies in animal models and, when possible, in the clinic. NDDs with a genetic basis have received particular attention. Transgenic animals that mimic genetic insults responsible for disease in man have provided insight about mechanisms of dysfunction, and, surprisingly, have shown that cognitive deficits can be addressed in adult animals. This review will present recent translational research based on animal models of genetic NDDs, as well as pharmacotherapeutic strategies under development to address deficits of brain function for Down syndrome, fragile X syndrome, Rett syndrome, neurofibromatosis-1, tuberous sclerosis, and autism. Although these disorders vary in underlying causes and clinical presentation, common pathways and mechanisms for dysfunction have been observed. These include abnormal gene dosage, imbalance among neurotransmitter systems, and deficits in the development, maintenance and plasticity of neuronal circuits. NDDs affect multiple brain systems and behaviors that may be amenable to drug therapies that target distinct deficits. A primary goal of translational research is to replace symptomatic and supportive drug therapies with pharmacotherapies based on a principled understanding of the causes of dysfunction. Based on this principle, several recently developed therapeutic strategies offer clear promise for clinical development in man.
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80
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Hanson JE, Madison DV. Imbalanced pattern completion vs. separation in cognitive disease: network simulations of synaptic pathologies predict a personalized therapeutics strategy. BMC Neurosci 2010; 11:96. [PMID: 20704756 PMCID: PMC2931521 DOI: 10.1186/1471-2202-11-96] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Accepted: 08/13/2010] [Indexed: 12/14/2022] Open
Abstract
Background Diverse Mouse genetic models of neurodevelopmental, neuropsychiatric, and neurodegenerative causes of impaired cognition exhibit at least four convergent points of synaptic malfunction: 1) Strength of long-term potentiation (LTP), 2) Strength of long-term depression (LTD), 3) Relative inhibition levels (Inhibition), and 4) Excitatory connectivity levels (Connectivity). Results To test the hypothesis that pathological increases or decreases in these synaptic properties could underlie imbalances at the level of basic neural network function, we explored each type of malfunction in a simulation of autoassociative memory. These network simulations revealed that one impact of impairments or excesses in each of these synaptic properties is to shift the trade-off between pattern separation and pattern completion performance during memory storage and recall. Each type of synaptic pathology either pushed the network balance towards intolerable error in pattern separation or intolerable error in pattern completion. Imbalances caused by pathological impairments or excesses in LTP, LTD, inhibition, or connectivity, could all be exacerbated, or rescued, by the simultaneous modulation of any of the other three synaptic properties. Conclusions Because appropriate modulation of any of the synaptic properties could help re-balance network function, regardless of the origins of the imbalance, we propose a new strategy of personalized cognitive therapeutics guided by assay of pattern completion vs. pattern separation function. Simulated examples and testable predictions of this theorized approach to cognitive therapeutics are presented.
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Affiliation(s)
- Jesse E Hanson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
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81
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Hewitt CA, Ling KH, Merson TD, Simpson KM, Ritchie ME, King SL, Pritchard MA, Smyth GK, Thomas T, Scott HS, Voss AK. Gene network disruptions and neurogenesis defects in the adult Ts1Cje mouse model of Down syndrome. PLoS One 2010; 5:e11561. [PMID: 20661276 PMCID: PMC2905390 DOI: 10.1371/journal.pone.0011561] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2010] [Accepted: 05/31/2010] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Down syndrome (DS) individuals suffer mental retardation with further cognitive decline and early onset Alzheimer's disease. METHODOLOGY/PRINCIPAL FINDINGS To understand how trisomy 21 causes these neurological abnormalities we investigated changes in gene expression networks combined with a systematic cell lineage analysis of adult neurogenesis using the Ts1Cje mouse model of DS. We demonstrated down regulation of a number of key genes involved in proliferation and cell cycle progression including Mcm7, Brca2, Prim1, Cenpo and Aurka in trisomic neurospheres. We found that trisomy did not affect the number of adult neural stem cells but resulted in reduced numbers of neural progenitors and neuroblasts. Analysis of differentiating adult Ts1Cje neural progenitors showed a severe reduction in numbers of neurons produced with a tendency for less elaborate neurites, whilst the numbers of astrocytes was increased. CONCLUSIONS/SIGNIFICANCE We have shown that trisomy affects a number of elements of adult neurogenesis likely to result in a progressive pathogenesis and consequently providing the potential for the development of therapies to slow progression of, or even ameliorate the neuronal deficits suffered by DS individuals.
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Affiliation(s)
- Chelsee A. Hewitt
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
- Department of Pathology, The Peter MacCallum Cancer Centre, Melbourne, Australia
| | - King-Hwa Ling
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
- Department of Molecular Pathology, The Centre for Cancer Biology, The Institute of Medical and Veterinary Science and The Hanson Institute, SA Pathology, and The Adelaide Cancer Research Institute, School of Medicine, University of Adelaide, Adelaide, Australia
- Department of Obstetrics and Gynaecology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Selangor, Malaysia
| | - Tobias D. Merson
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Ken M. Simpson
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Matthew E. Ritchie
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Sarah L. King
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Melanie A. Pritchard
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
| | - Gordon K. Smyth
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Tim Thomas
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
| | - Hamish S. Scott
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
- Department of Molecular Pathology, The Centre for Cancer Biology, The Institute of Medical and Veterinary Science and The Hanson Institute, SA Pathology, and The Adelaide Cancer Research Institute, School of Medicine, University of Adelaide, Adelaide, Australia
| | - Anne K. Voss
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
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82
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Netzer WJ, Powell C, Nong Y, Blundell J, Wong L, Duff K, Flajolet M, Greengard P. Lowering beta-amyloid levels rescues learning and memory in a Down syndrome mouse model. PLoS One 2010; 5:e10943. [PMID: 20532168 PMCID: PMC2880593 DOI: 10.1371/journal.pone.0010943] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Accepted: 05/11/2010] [Indexed: 02/04/2023] Open
Abstract
β-amyloid levels are elevated in Down syndrome (DS) patients throughout life and are believed to cause Alzheimer's disease (AD) in adult members of this population. However, it is not known if β-amyloid contributes to intellectual disability in younger individuals. We used a γ-secretase inhibitor to lower β-amyloid levels in young mice that model DS. This treatment corrected learning deficits characteristic of these mice, suggesting that β-amyloid-lowering therapies might improve cognitive function in young DS patients.
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Affiliation(s)
- William J Netzer
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, New York, USA.
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83
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Delabar JM. [New perspectives on molecular and genic therapies in Down syndrome]. Med Sci (Paris) 2010; 26:371-6. [PMID: 20412741 DOI: 10.1051/medsci/2010264371] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Trisomy 21 was first described as a syndrome in the middle of the nineteenth century and associated to a chromosomic anomaly one hundred years later: the most salient feature of this syndrome is a mental retardation of variable intensity. Molecular mapping and DNA sequencing have allowed identifying the gene content of chromosome 21. Molecular quantitative analyses indicated that trisomy is inducing an overexpression for a large part of the triplicated genes and deregulates also pathways involving non HSA21 genes. Together with the physiological description of murine models overexpressing orthologous genes, these data have allowed to elaborate hypotheses on the cause of cognitive impairment. From these hypotheses and using murine models it is now possible to assess the efficiency of various therapeutic strategies. This paper reviews these new perspectives starting from the strategies targeting the level of HSA21 RNAs or HSA21 proteins; then it describes methods targeting activities either of proteins involved in cell cycle pathways or of proteins controlling the synaptic plasticity. It is promising that strategies targeting specific genes or specific pathways are already giving positive results.
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Affiliation(s)
- Jean Maurice Delabar
- Unité de biologie fonctionnelle et adaptative (BFA), EAC CNRS 4413, Université Paris Diderot, Marie-Andrée Lagroua-Weill-Hallé, bâtiment Lamarck, 75205 Paris, France.
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84
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Reversibility of functional deficits in experimental models of Rett syndrome. Biochem Soc Trans 2010; 38:498-506. [DOI: 10.1042/bst0380498] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Mutations in the X-linked MECP2 gene are the primary cause of the severe autism spectrum disorder RTT (Rett syndrome). Deletion of Mecp2 in mice recapitulates many of the overt neurological features seen in humans, and the delayed onset of symptoms is accompanied by deficits in neuronal morphology and synaptic physiology. Recent evidence suggests that reactivation of endogenous Mecp2 in young and adult mice can reverse aspects of RTT-like pathology. In the current perspective, we discuss these findings as well as other genetic, pharmacological and environmental interventions that attempt phenotypic rescue in RTT. We believe these studies provide valuable insights into the tractability of RTT and related conditions and are useful pointers for the development of future therapeutic strategies.
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85
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Ruparelia A, Wiseman F, Sheppard O, Tybulewicz VL, Fisher EM. Down syndrome and the molecular pathogenesis resulting from trisomy of human chromosome 21. J Biomed Res 2010; 24:87-99. [PMID: 23554618 PMCID: PMC3596542 DOI: 10.1016/s1674-8301(10)60016-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Indexed: 01/12/2023] Open
Abstract
Chromosome copy number aberrations, anueploidies, are common in the human population but generally lethal. However, trisomy of human chromosome 21 is compatible with life and people born with this form of aneuploidy manifest the features of Down syndrome, named after Langdon Down who was a 19(th) century British physician who first described a group of people with this disorder. Down syndrome includes learning and memory deficits in all cases, as well as many other features which vary in penetrance and expressivity in different people. While Down syndrome clearly has a genetic cause - the extra dose of genes on chromosome 21 - we do not know which genes are important for which aspects of the syndrome, which biochemical pathways are disrupted, or, generally how design therapies to ameliorate the effects of these disruptions. Recently, with new insights gained from studying mouse models of Down syndrome, specific genes and pathways are being shown to be involved in the pathogenesis of the disorder. This is opening the way for exciting new studies of potential therapeutics for aspects of Down syndrome, particularly the learning and memory deficits.
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Affiliation(s)
- Aarti Ruparelia
- Department of Neurodegenerative Disease, UCL Institute of Neurology, Queen Square, London, UK
| | - Frances Wiseman
- Department of Neurodegenerative Disease, UCL Institute of Neurology, Queen Square, London, UK
| | - Olivia Sheppard
- Department of Neurodegenerative Disease, UCL Institute of Neurology, Queen Square, London, UK
| | | | - Elizabeth M.C. Fisher
- Department of Neurodegenerative Disease, UCL Institute of Neurology, Queen Square, London, UK
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86
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Rachidi M, Lopes C. Molecular and cellular mechanisms elucidating neurocognitive basis of functional impairments associated with intellectual disability in Down syndrome. AMERICAN JOURNAL ON INTELLECTUAL AND DEVELOPMENTAL DISABILITIES 2010; 115:83-112. [PMID: 20441388 DOI: 10.1352/1944-7558-115.2.83] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2008] [Accepted: 11/05/2009] [Indexed: 05/29/2023]
Abstract
Down syndrome, the most common genetic cause of intellectual disability, is associated with brain disorders due to chromosome 21 gene overdosage. Molecular and cellular mechanisms involved in the neuromorphological alterations and cognitive impairments are reported herein in a global model. Recent advances in Down syndrome research have lead to the identification of altered molecular pathways involved in intellectual disability, such as Calcineurin/NFATs pathways, that are of crucial importance in understanding the molecular basis of intellectual disability pathogenesis in this syndrome. Potential treatments in mouse models of Down syndrome, including antagonists of NMDA or GABA(A) receptors, and microRNAs provide new avenues to develop treatments of intellectual disability. Nevertheless, understanding the links between molecular pathways and treatment strategies in human beings requires further research.
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Affiliation(s)
- Mohammed Rachidi
- University of Paris, Denis Diderot Laboratory of Genetic Dysregulation Models: Trisomy 21 and Hyperhomocysteinemia. Tour 54, Paris, France.
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87
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Gardiner KJ. Molecular basis of pharmacotherapies for cognition in Down syndrome. Trends Pharmacol Sci 2010; 31:66-73. [PMID: 19963286 PMCID: PMC2815198 DOI: 10.1016/j.tips.2009.10.010] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Revised: 10/27/2009] [Accepted: 10/30/2009] [Indexed: 12/18/2022]
Abstract
Intellectual disability in Down syndrome (DS) ranges from low normal to severely impaired and has a significant impact on the quality-of-life of the individuals affected and their families. Because the incidence of DS remains at approximately 1 in 700 live births and the lifespan is now >50 years, development of pharmacotherapies for cognitive deficits is an important goal. DS is due to an extra copy of human chromosome 21 and has often been considered too complex a genetic abnormality to be amenable to intervention. However, recent successes in rescuing learning/memory impairments in a mouse model of DS suggest that this negative outlook may not be justified. In this contribution, we first review the DS phenotype, chromosome 21 gene content and mouse models. We then discuss recent successes and the remaining challenges in the identification of targets for and preclinical evaluation of potential therapeutics.
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Affiliation(s)
- Katheleen J Gardiner
- Department of Pediatrics, Intellectual and Developmental Disability Research Center, Human Medical Genetics and Neuroscience Programs, University of Colorado Denver, 12800 E 19(th) Avenue, Aurora, Colorado 80045, USA.
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88
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Communication breaks-Down: from neurodevelopment defects to cognitive disabilities in Down syndrome. Prog Neurobiol 2010; 91:1-22. [PMID: 20097253 DOI: 10.1016/j.pneurobio.2010.01.003] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2009] [Revised: 12/10/2009] [Accepted: 01/14/2010] [Indexed: 12/31/2022]
Abstract
Down syndrome (DS) is the leading cause of genetically-defined intellectual disability and congenital birth defects. Despite being one of the first genetic diseases identified, only recently, thanks to the phenotypic analysis of DS mouse genetic models, we have begun to understand how trisomy may impact cognitive function. Cognitive disabilities in DS appear to result mainly from two pathological processes: neurogenesis impairment and Alzheimer-like degeneration. In DS brain, suboptimal network architecture and altered synaptic communication arising from neurodevelopmental impairment are key determinants of cognitive defects. Hypocellularity and hypoplasia start at early developmental stages and likely depend upon impaired proliferation of neuronal precursors, resulting in reduction of numbers of neurons and synaptic contacts. The impairment of neuronal precursor proliferation extends to adult neurogenesis and may affect learning and memory. Neurodegenerative mechanisms also contribute to DS cognitive impairment. Early onset Alzheimer disease occurs with extremely high incidence in DS patients and is causally-related to overexpression of beta-amyloid precursor protein (betaAPP), which is one of the triplicated genes in DS. In this review, we will survey the available findings on neurodevelopmental and neurodegenerative changes occurring in DS throughout life. Moreover, we will discuss the potential mechanisms by which defects in neurogenesis and neurodegenerative processes lead to altered formation of neural circuits and impair cognitive function, in connection with findings on pharmacological treatments of potential benefit for DS.
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89
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Cramer NP, Best TK, Stoffel M, Siarey RJ, Galdzicki Z. GABAB–GIRK2-Mediated Signaling in Down Syndrome. GABABRECEPTOR PHARMACOLOGY - A TRIBUTE TO NORMAN BOWERY 2010; 58:397-426. [DOI: 10.1016/s1054-3589(10)58015-3] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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90
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Han F, Yu H, Zhang J, Tian C, Schmidt C, Nava C, Davisson MT, Zheng QY. Otitis media in a mouse model for Down syndrome. Int J Exp Pathol 2009; 90:480-8. [PMID: 19765102 DOI: 10.1111/j.1365-2613.2009.00677.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The Ts65Dn mouse shares many phenotypic characteristics of human Down syndrome. Here, we report that otitis media, characterized by effusion in the middle ear and hearing loss, was prevalent in Ts65Dn mice. Of the 53 Ts65Dn mice tested, 81.1% had high auditory-evoked brainstem response (ABR) thresholds for at least one of the stimulus frequencies (click, 8 kHz, 16 kHz and 32 kHz), in at least one ear. The ABR thresholds were variable and showed no tendency toward increase with age, from 2 to 7 months of age. Observation of pathology in mice, aged 3-4 months, revealed middle ear effusion in 11 of 15 Ts65Dn mice examined, but only in two of 11 wild-type mice. The effusion in each mouse varied substantially in volume and inflammatory cell content. The middle ear mucosae were generally thickened and goblet cells were distributed with higher density in the epithelium of the middle ear cavity of Ts65Dn mice as compared with those of wild-type controls. Bacteria of pathogenic importance to humans also were identified in the Ts65Dn mice. This is the first report of otitis media in the Ts65Dn mouse as a model characteristic of human Down syndrome.
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Affiliation(s)
- Fengchan Han
- Department of Otolaryngology-HNS, Case Western Reserve University, Cleveland, OH 44106, USA
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91
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Costa ACS, Stasko MR, Schmidt C, Davisson MT. Behavioral validation of the Ts65Dn mouse model for Down syndrome of a genetic background free of the retinal degeneration mutation Pde6b(rd1). Behav Brain Res 2009; 206:52-62. [PMID: 19720087 DOI: 10.1016/j.bbr.2009.08.034] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Revised: 08/22/2009] [Accepted: 08/27/2009] [Indexed: 02/03/2023]
Abstract
The Ts65Dn mouse is the most studied and complete aneuploid model of Down syndrome (DS) widely available. As a model for human trisomy 21, these mice display many attractive features, including performance deficits in different behavioral tasks, alterations in synaptic plasticity and adult neurogenesis, motor dysfunction, and age-dependent cholinergic neurodegeneration. Currently, Ts65Dn mice are maintained on a genetic background that leads to blindness in about 25% of their offspring, because it segregates for the retinal degeneration 1 (Pde6b(rd1)) mutation of C3H/HeSnJ. This means that 25% of the mice have to be discarded in most experiments involving these animals, which is particularly problematic because the Ts65Dn stock has low reproductive performance. To circumvent this problem, we have bred the Ts65Dn extra chromosome many generations into a closely related genetic background that does not carry the Pde6b(rd1) mutation. Although the new genetic background is expected to be nearly identical to the original, differences in genetic background have the potential to alter mouse performance in certain behavioral tests. Therefore, we designed the present study primarily as a behavioral validation of Ts65Dn mice of the new background. We compared side-by-side their performance with that of Ts65Dn mice of the original background on the following set of assessments: (1) body length and weight; (2) 24-h locomotor activity; (3) the Morris water maze; (4) fear conditioning; and (5) grip strength. Except for very subtle differences on water maze performance, we found no significant differences between Ts65Dn mice on the two backgrounds in the measures assessed.
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Affiliation(s)
- Alberto C S Costa
- Division of Clinical Pharmacology and Toxicology, Department of Medicine, University of Colorado Denver School of Medicine, Aurora, CO 80045, USA.
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92
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Dierssen M, Herault Y, Estivill X. Aneuploidy: from a physiological mechanism of variance to Down syndrome. Physiol Rev 2009; 89:887-920. [PMID: 19584316 DOI: 10.1152/physrev.00032.2007] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Quantitative differences in gene expression emerge as a significant source of variation in natural populations, representing an important substrate for evolution and accounting for a considerable fraction of phenotypic diversity. However, perturbation of gene expression is also the main factor in determining the molecular pathogenesis of numerous aneuploid disorders. In this review, we focus on Down syndrome (DS) as the prototype of "genomic disorder" induced by copy number change. The understanding of the pathogenicity of the extra genomic material in trisomy 21 has accelerated in the last years due to the recent advances in genome sequencing, comparative genome analysis, functional genome exploration, and the use of model organisms. We present recent data on the role of genome-altering processes in the generation of diversity in DS neural phenotypes focusing on the impact of trisomy on brain structure and mental retardation and on biological pathways and cell types in target brain regions (including prefrontal cortex, hippocampus, cerebellum, and basal ganglia). We also review the potential that genetically engineered mouse models of DS bring into the understanding of the molecular biology of human learning disorders.
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Affiliation(s)
- Mara Dierssen
- Genes and Disease Program, Genomic Regulation Center-CRG, Pompeu Fabra University, Barcelona Biomedical Research Park, Dr Aiguader 88, PRBB building E, Barcelona 08003, Catalonia, Spain.
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93
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Adult reversal of cognitive phenotypes in neurodevelopmental disorders. J Neurodev Disord 2009; 1:150-7. [PMID: 19812701 PMCID: PMC2755132 DOI: 10.1007/s11689-009-9018-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Accepted: 05/18/2009] [Indexed: 02/07/2023] Open
Abstract
Recent findings in mice suggest that it is possible to reverse certain neurodevelopmental disorders in adults. Changes in development, previously thought to be irreparable in adults, were believed to underlie the neurological and psychiatric phenotypes of a range of common mental health problems with a clear developmental component. As a consequence, most researchers have focused their efforts on understanding the molecular and cellular processes that alter development with the hope that early intervention could prevent the emergent pathology. Unexpectedly, several different animal model studies published recently, including animal models of autism, suggest that it may be possible to reverse neurodevelopmental disorders in adults: Addressing the underlying molecular and cellular deficits in adults could in several cases dramatically improve the neurocognitive phenotypes in these animal models. The findings reviewed here provide hope to millions of individuals afflicted with a wide range of neurodevelopmental disorders, including autism, since they suggest that it may be possible to treat or even cure them in adults.
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94
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Patterson D. Molecular genetic analysis of Down syndrome. Hum Genet 2009; 126:195-214. [PMID: 19526251 DOI: 10.1007/s00439-009-0696-8] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Accepted: 05/29/2009] [Indexed: 12/18/2022]
Abstract
Down syndrome (DS) is caused by trisomy of all or part of human chromosome 21 (HSA21) and is the most common genetic cause of significant intellectual disability. In addition to intellectual disability, many other health problems, such as congenital heart disease, Alzheimer's disease, leukemia, hypotonia, motor disorders, and various physical anomalies occur at an elevated frequency in people with DS. On the other hand, people with DS seem to be at a decreased risk of certain cancers and perhaps of atherosclerosis. There is wide variability in the phenotypes associated with DS. Although ultimately the phenotypes of DS must be due to trisomy of HSA21, the genetic mechanisms by which the phenotypes arise are not understood. The recent recognition that there are many genetically active elements that do not encode proteins makes the situation more complex. Additional complexity may exist due to possible epigenetic changes that may act differently in DS. Numerous mouse models with features reminiscent of those seen in individuals with DS have been produced and studied in some depth, and these have added considerable insight into possible genetic mechanisms behind some of the phenotypes. These mouse models allow experimental approaches, including attempts at therapy, that are not possible in humans. Progress in understanding the genetic mechanisms by which trisomy of HSA21 leads to DS is the subject of this review.
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Affiliation(s)
- David Patterson
- Eleanor Roosevelt Institute, University of Denver, 2101 E. Wesley Avenue, Denver, CO 80208-6600, USA.
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95
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Preclinical assessment of proconvulsant drug activity and its relevance for predicting adverse events in humans. Eur J Pharmacol 2009; 610:1-11. [DOI: 10.1016/j.ejphar.2009.03.025] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Revised: 02/19/2009] [Accepted: 03/03/2009] [Indexed: 12/20/2022]
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96
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Abstract
Abnormalities in brain development, thought to be irreversible in adults, have long been assumed to underlie the neurological and psychiatric symptoms associated with neurodevelopmental disorders. Surprisingly, a number of recent animal model studies of neurodevelopmental disorders demonstrate that reversing the underlying molecular deficits can result in substantial improvements in function even if treatments are started in adulthood. These findings mark a paradigmatic change in the way we understand and envision treating neurodevelopmental disorders.
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Affiliation(s)
- Dan Ehninger
- Departments of Neurobiology, Psychiatry and Biobehavioral Sciences, Psychology and the Brain Research Institute, University of California, Los Angeles, 695 Charles Young Drive South, Los Angeles, CA 90095-1761, USA
| | - Weidong Li
- Departments of Neurobiology, Psychiatry and Biobehavioral Sciences, Psychology and the Brain Research Institute, University of California, Los Angeles, 695 Charles Young Drive South, Los Angeles, CA 90095-1761, USA
| | - Kevin Fox
- Cardiff School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3US, UK
| | - Michael P. Stryker
- Department of Physiology, W.M. Keck Foundation Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA 94143-0444, USA
| | - Alcino J. Silva
- Departments of Neurobiology, Psychiatry and Biobehavioral Sciences, Psychology and the Brain Research Institute, University of California, Los Angeles, 695 Charles Young Drive South, Los Angeles, CA 90095-1761, USA
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97
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Cui Y, Costa RM, Murphy GG, Elgersma Y, Zhu Y, Gutmann DH, Parada LF, Mody I, Silva AJ. Neurofibromin regulation of ERK signaling modulates GABA release and learning. Cell 2008; 135:549-60. [PMID: 18984165 DOI: 10.1016/j.cell.2008.09.060] [Citation(s) in RCA: 335] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Revised: 05/02/2008] [Accepted: 09/08/2008] [Indexed: 11/17/2022]
Abstract
We uncovered a role for ERK signaling in GABA release, long-term potentiation (LTP), and learning, and show that disruption of this mechanism accounts for the learning deficits in a mouse model for learning disabilities in neurofibromatosis type I (NF1). Our results demonstrate that neurofibromin modulates ERK/synapsin I-dependent GABA release, which in turn modulates hippocampal LTP and learning. An Nf1 heterozygous null mutation, which results in enhanced ERK and synapsin I phosphorylation, increased GABA release in the hippocampus, and this was reversed by pharmacological downregulation of ERK signaling. Importantly, the learning deficits associated with the Nf1 mutation were rescued by a subthreshold dose of a GABA(A) antagonist. Accordingly, Cre deletions of Nf1 showed that only those deletions involving inhibitory neurons caused hippocampal inhibition, LTP, and learning abnormalities. Importantly, our results also revealed lasting increases in GABA release triggered by learning, indicating that the mechanisms uncovered here are of general importance for learning.
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Affiliation(s)
- Yijun Cui
- Department of Neurobiology, Brain Research Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA
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98
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Siddiqui A, Lacroix T, Stasko MR, Scott-McKean JJ, Costa AC, Gardiner KJ. Molecular responses of the Ts65Dn and Ts1Cje mouse models of Down syndrome to MK-801. GENES, BRAIN, AND BEHAVIOR 2008; 7:810-20. [PMID: 19125866 PMCID: PMC2677016 DOI: 10.1111/j.1601-183x.2008.00428.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Down syndrome (DS), caused by trisomy of human chromosome 21 (chr21), is the most common genetic cause of intellectual disability. The Ts65Dn mouse model of DS is trisomic for orthologs of 94 chr21-encoded, confirmed protein-coding genes and displays a number of behavioral deficits. Recently, Ts65Dn mice were shown to be hypersensitive to the locomotor stimulatory effects of the high-affinity N-methyl-d-aspartate (NMDA) receptor (NMDAR) channel blocker, MK-801. This is consistent with the functions of several chr21 proteins that are predicted directly or indirectly to impact NMDAR function or NMDAR-mediated signaling. In this study, we show that a second mouse model of DS, the Ts1Cje, which is trisomic for 70 protein-coding genes, is also hypersensitive to MK-801. To investigate the molecular basis for the responses to MK-801, we have measured levels of a subset of chr21 and phosphorylated non-chr21 proteins, in the cortex and hippocampus of Ts65Dn and Ts1Cje mice and euploid controls, with and without treatment with MK-801. We show that in euploid mice, the chr21-encoded proteins, TIAM1 and DYRK1A, and phosphorylation of AKT, ERK1/2 and the transcription factor ELK are involved in the MK-801 response. However, in both Ts65Dn and Ts1Cje mice, levels of phosphorylation are constitutively elevated in naïve, unstimulated mice, and the MK-801-induced changes in TIAM1 and DYRK1A and in phosphorylation are either absent or abnormal, with both genotype and brain-region-specific patterns. These results emphasize the complexities of the pathway perturbations that arise with segmental trisomy.
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Affiliation(s)
| | | | - Melissa R. Stasko
- Department of Medicine, Division of Clinical Pharmacology and Toxicology
| | | | - Alberto C.S. Costa
- Department of Medicine, Division of Clinical Pharmacology and Toxicology
- Neuroscience Program
| | - Katheleen J. Gardiner
- Department of Pediatrics
- Human Medical Genetics Program, University of Colorado Denver
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