101
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Dickendesher TL, Baldwin KT, Mironova YA, Koriyama Y, Raiker SJ, Askew KL, Wood A, Geoffroy CG, Zheng B, Liepmann CD, Katagiri Y, Benowitz LI, Geller HM, Giger RJ. NgR1 and NgR3 are receptors for chondroitin sulfate proteoglycans. Nat Neurosci 2012; 15:703-12. [PMID: 22406547 PMCID: PMC3337880 DOI: 10.1038/nn.3070] [Citation(s) in RCA: 341] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 02/06/2012] [Indexed: 12/17/2022]
Abstract
In the adult mammalian CNS, chondroitin sulfate proteoglycans (CSPGs) and myelin–associated inhibitors (MAIs) stabilize neuronal structure and restrict compensatory sprouting following injury. The Nogo receptor family members NgR1 and NgR2 bind to MAIs and have been implicated in neuronal inhibition. Here we show that NgR1 and NgR3 bind with high–affinity to the glycosaminoglycan moiety of proteoglycans and participate in CSPG inhibition in cultured neurons. Nogo receptor triple mutants (NgR123−/−), but not single mutants, show enhanced axonal regeneration following retro–orbital optic nerve crush injury. The combined loss of NgR1 and NgR3 (NgR13−/−), but not NgR1 and NgR2 (NgR12−/−), is sufficient to mimic the NgR123−/− regeneration phenotype. Regeneration in NgR13−/− mice is further enhanced by simultaneous ablation of RPTPσ, a known CSPG receptor. Collectively, these results identify NgR1 and NgR3 as novel CSPG receptors, demonstrate functional redundancy among CSPG receptors, and provide unexpected evidence for shared mechanisms of MAI and CSPG inhibition.
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Affiliation(s)
- Travis L Dickendesher
- Neuroscience Program, University of Michigan School of Medicine, Ann Arbor, Michigan, USA
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102
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The Nogo-66 receptor family in the intact and diseased CNS. Cell Tissue Res 2012; 349:105-17. [PMID: 22311207 DOI: 10.1007/s00441-012-1332-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 01/16/2012] [Indexed: 10/14/2022]
Abstract
The Nogo-66 receptor family (NgR) consists in three glycophosphatidylinositol (GPI)-anchored receptors (NgR1, NgR2 and NgR3), which are primarily expressed by neurons in the central and peripheral mammalian nervous system. NgR1 was identified as serving as a high affinity binding protein for the three classical myelin-associated inhibitors (MAIs) Nogo-A, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp), which limit axon regeneration and sprouting in the injured brain. Recent studies suggest that NgR signaling may also play an essential role in the intact adult CNS in restricting axonal and synaptic plasticity and are involved in neurodegenerative diseases, particularly in Alzheimer's disease pathology through modulation of β-secretase cleavage. Here, we outline the biochemical properties of NgRs and their functional roles in the intact and diseased CNS.
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103
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Zhu Y, Wang X, Ye X, Gao C, Wang W. Effects of electroacupuncture on the expression of p70 ribosomal protein S6 kinase and ribosomal protein S6 in the hippocampus of rats with vascular dementia. Neural Regen Res 2012; 7:207-11. [PMID: 25767501 PMCID: PMC4353116 DOI: 10.3969/j.issn.1673-5374.2012.03.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2011] [Accepted: 11/12/2011] [Indexed: 02/02/2023] Open
Abstract
This study investigated the mechanism underlying electroacupuncture therapy for vascular dementia through electroacupuncture at the acupoints of Baihui (DU20), Dazhui (DU14), and bilateral Shenshu (BL23) in a rat model of vascular dementia produced by bilateral middle cerebral artery occlusion. Morris water maze test showed that electroacupuncture improved the learning ability of vascular dementia rats. Western blot assay revealed that the expression of p70 ribosomal protein S6 kinase and ribosomal protein S6 in vascular dementia rats was significantly increased after electroacupuncture, compared with the model group that was not treated with acupuncture. The average escape latency was also shortened after electroacupuncture, and escape strategies in the spatial probe test improved from edge and random searches, to linear and trending swim pathways. The experimental findings indicate that electroacupuncture improves learning and memory ability by up-regulating expression of p70 ribosomal protein S6 kinase and ribosomal protein S6 in the hippocampus of vascular dementia rats.
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Affiliation(s)
- Yanzhen Zhu
- Department of Integrative Medicine, Fujian University of Traditional Chinese Medicine, Fuzhou 350108, Fujian Province, China
| | - Xuan Wang
- Department of Acupuncture and Tuina, Fujian University of Traditional Chinese Medicine, Fuzhou 350108, Fujian Province, China
| | - Xiaobao Ye
- Department of Integrative Medicine, Fujian University of Traditional Chinese Medicine, Fuzhou 350108, Fujian Province, China
| | - Changhua Gao
- Department of Integrative Medicine, Fujian University of Traditional Chinese Medicine, Fuzhou 350108, Fujian Province, China
| | - Wei Wang
- Center of Neurobiology, Fujian Medical University, Fuzhou 350108, Fujian Province, China
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104
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Chinese Medicine's Intervention Effect on Nogo-A/NgR. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2012; 2012:528482. [PMID: 22216056 PMCID: PMC3247900 DOI: 10.1155/2012/528482] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Revised: 09/28/2011] [Accepted: 11/02/2011] [Indexed: 01/31/2023]
Abstract
Cerebral vascular disease is very common in the elderly and is one of the most dangerous diseases which is hazardous to the body's health, and it is the medical specialists' study hot spot not only in the clinical field but also in the medical basic research field. Neural regeneration has been paid more and more attention in recent years. Nogo's function in the process of neural regeneration has become the focal point since it was discovered in the year 2000. Many studies elucidate that Nogo negatively affects the neural regeneration and plasticity. Chinese medicine plays an important role in the prevention and treatment of neural diseases, and recently some researches about the Chinese medicine's intervention effect on Nogo-A/NgR sprang up, so it is necessary to make a review on this aspect.
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105
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Peng X, Kim J, Zhou Z, Fink DJ, Mata M. Neuronal Nogo-A regulates glutamate receptor subunit expression in hippocampal neurons. J Neurochem 2011; 119:1183-93. [PMID: 21985178 DOI: 10.1111/j.1471-4159.2011.07520.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Nogo-A and its cognate receptor NogoR1 (NgR1) are both expressed in neurons. To explore the function of these proteins in neurons of the CNS, we carried out a series of studies using postnatal hippocampal neurons in culture. Interfering with the binding of Nogo-A to NgR1 either by adding truncated soluble fragment of NgR1 (NgSR) or by reducing NgR1 protein with a specific siRNA, resulted in a marked reduction in Nogo-A expression. Inhibition of Rho-ROCK or MEK-MAPK signaling resulted in a similar reduction in neuronal Nogo-A mRNA and protein. Reducing Nogo-A protein levels by siRNA resulted in an increase in the post-synaptic scaffolding protein PSD95, as well as increases in GluA1/GluA2 AMPA receptor and GluN1/GluN2A/GluN2B NMDA glutamate receptor subunits. siRNA treatment to reduce Nogo-A resulted in phosphorylation of mTOR; addition of rapamycin to block mTOR signaling prevented the up-regulation in glutamate receptor subunits. siRNA reduction of NgR1 resulted in increased expression of the same glutamate receptor subunits. Taken together the results suggest that transcription and translation of Nogo-A in hippocampal neurons is regulated by a signaling through NgR1, and that interactions between neuronal Nogo-A and NgR1 regulate glutamatergic transmission by altering NMDA and AMPA receptor levels through an rapamycin-sensitive mTOR-dependent translation mechanism.
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Affiliation(s)
- Xiangmin Peng
- Department of Neurology, University of Michigan and VA Ann Arbor Healthcare System, Ann Arbor, Michigan 48109, USA
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106
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Ferraro GB, Morrison CJ, Overall CM, Strittmatter SM, Fournier AE. Membrane-type matrix metalloproteinase-3 regulates neuronal responsiveness to myelin through Nogo-66 receptor 1 cleavage. J Biol Chem 2011; 286:31418-24. [PMID: 21768085 DOI: 10.1074/jbc.m111.249169] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Nogo-66 receptor 1 (NgR1) is a glycosylphosphatidylinositol-anchored receptor for myelin-associated inhibitors that restricts plasticity and axonal regrowth in the CNS. NgR1 is cleaved from the cell surface of SH-SY5Y neuroblastoma cells in a metalloproteinase-dependent manner; however, the mechanism and physiological consequence of NgR1 shedding have not been explored. We now demonstrate that NgR1 is shed from multiple populations of primary neurons. Through a loss-of-function approach, we found that membrane-type matrix metalloproteinase-3 (MT3-MMP) regulates endogenous NgR1 shedding in primary neurons. Neuronal knockdown of MT3-MMP resulted in the accumulation of NgR1 at the cell surface and reduced the accumulation of the NgR1 cleavage fragment in medium conditioned by cortical neurons. Recombinant MT1-, MT2-, MT3-, and MT5-MMPs promoted NgR1 shedding from the surface of primary neurons, and this treatment rendered neurons resistant to myelin-associated inhibitors. Introduction of a cleavage-resistant form of NgR1 reconstitutes the neuronal response to these inhibitors, demonstrating that specific metalloproteinases attenuate neuronal responses to myelin in an NgR1-dependent manner.
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Affiliation(s)
- Gino B Ferraro
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, Montreal, Quebec H3A 2B4, Canada
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107
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de Wit J, Hong W, Luo L, Ghosh A. Role of leucine-rich repeat proteins in the development and function of neural circuits. Annu Rev Cell Dev Biol 2011; 27:697-729. [PMID: 21740233 DOI: 10.1146/annurev-cellbio-092910-154111] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The nervous system consists of an ensemble of billions of neurons interconnected in a highly specific pattern that allows proper propagation and integration of neural activities. The organization of these specific connections emerges from sequential developmental events including axon guidance, target selection, and synapse formation. These events critically rely on cell-cell recognition and communication mediated by cell-surface ligands and receptors. Recent studies have uncovered central roles for leucine-rich repeat (LRR) domain-containing proteins, not only in organizing neural connectivity from axon guidance to target selection to synapse formation, but also in various nervous system disorders. Their versatile LRR domains, in particular, serve as key sites for interactions with a wide diversity of binding partners. Here, we focus on a few exquisite examples of secreted or membrane-associated LRR proteins in Drosophila and mammals and review the mechanisms by which they regulate diverse aspects of nervous system development and function.
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Affiliation(s)
- Joris de Wit
- Neurobiology Section, Division of Biology, University of California, San Diego, La Jolla, California 92093-0366, USA
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108
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Myelin associated inhibitors: a link between injury-induced and experience-dependent plasticity. Exp Neurol 2011; 235:43-52. [PMID: 21699896 DOI: 10.1016/j.expneurol.2011.06.006] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2011] [Revised: 04/26/2011] [Accepted: 06/07/2011] [Indexed: 01/01/2023]
Abstract
In the adult, both neurologic recovery and anatomical growth after a CNS injury are limited. Two classes of growth inhibitors, myelin associated inhibitors (MAIs) and extracellular matrix associated inhibitors, limit both functional recovery and anatomical rearrangements in animal models of spinal cord injury. Here we focus on how MAIs limit a wide spectrum of growth that includes regeneration, sprouting, and plasticity in both the intact and lesioned CNS. Three classic myelin associated inhibitors, Nogo-A, MAG, and OMgp, signal through their common receptors, Nogo-66 Receptor-1 (NgR1) and Paired-Immunoglobulin-like-Receptor-B (PirB), to regulate cytoskeletal dynamics and inhibit growth. Initially described as inhibitors of axonal regeneration, subsequent work has demonstrated that MAIs also limit activity and experience-dependent plasticity in the intact, adult CNS. MAIs therefore represent a point of convergence for plasticity that limits anatomical rearrangements regardless of the inciting stimulus, blurring the distinction between injury studies and more "basic" plasticity studies.
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109
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Lee JK, Zheng B. Role of myelin-associated inhibitors in axonal repair after spinal cord injury. Exp Neurol 2011; 235:33-42. [PMID: 21596039 DOI: 10.1016/j.expneurol.2011.05.001] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2010] [Revised: 04/19/2011] [Accepted: 05/01/2011] [Indexed: 12/15/2022]
Abstract
Myelin-associated inhibitors of axon growth, including Nogo, MAG and OMgp, have been the subject of intense research. A myriad of experimental approaches have been applied to investigate the potential of targeting these molecules to promote axonal repair after spinal cord injury. However, there are still conflicting results on their role in axon regeneration and therefore a lack of a cohesive mechanism on how these molecules can be targeted to promote axon repair. One major reason may be the lack of a clear definition of axon regeneration in the first place. Nevertheless, recent data from genetic studies in mice indicate that the roles of these molecules in CNS axon repair may be more intricate than previously envisioned.
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Affiliation(s)
- Jae K Lee
- University of California San Diego, Department of Neurosciences, 9500 Gilman Drive, MC 0691, La Jolla, CA 92093-0691, USA.
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110
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Starkey ML, Schwab ME. Anti-Nogo-A and training: can one plus one equal three? Exp Neurol 2011; 235:53-61. [PMID: 21530508 DOI: 10.1016/j.expneurol.2011.04.008] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Revised: 03/15/2011] [Accepted: 04/07/2011] [Indexed: 12/14/2022]
Abstract
Following spinal cord injury (SCI) the adult central nervous system (CNS) has a limited but substantial capacity for repair and plastic reorganisation. The degree of reorganisation is determined by a number of factors such as the extent and location of the lesion, the remaining circuit activity within the CNS and the age at injury. However, even in the best cases this spontaneous reorganisation does not lead to full recovery of the affected behaviour but instead often results in a functionally successful but compensatory strategy. Current SCI research focuses on enhancing fibre tract (re-)growth and recovery processes. Two currently promising approaches are the neutralisation of CNS growth inhibitory factors, and rehabilitative training of remaining networks. Independently, both approaches can lead to substantial functional recovery and anatomical reorganisation. In this review we focus on Nogo-A, a neurite growth inhibitory protein present in the adult CNS, and its role in regenerative and plastic growth following SCI. We then discuss the efforts of rehabilitative training and the potential combination of the two therapies.
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Affiliation(s)
- Michelle L Starkey
- Brain Research Institute, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
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111
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VanGuilder HD, Farley JA, Yan H, Van Kirk CA, Mitschelen M, Sonntag WE, Freeman WM. Hippocampal dysregulation of synaptic plasticity-associated proteins with age-related cognitive decline. Neurobiol Dis 2011; 43:201-12. [PMID: 21440628 DOI: 10.1016/j.nbd.2011.03.012] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Accepted: 03/18/2011] [Indexed: 12/16/2022] Open
Abstract
Age-related cognitive decline occurs without frank neurodegeneration and is the most common cause of memory impairment in aging individuals. With increasing longevity, cognitive deficits, especially in hippocampus-dependent memory processes, are increasing in prevalence. Nevertheless, the neurobiological basis of age-related cognitive decline remains unknown. While concerted efforts have led to the identification of neurobiological changes with aging, few age-related alterations have been definitively correlated to behavioral measures of cognitive decline. In this work, adult (12 months) and aged (28 months) rats were categorized by Morris water maze performance as Adult cognitively Intact, Aged cognitively Intact or Aged cognitively Impaired, and protein expression was examined in hippocampal synaptosome preparations. Previously described differences in synaptic expression of neurotransmission-associated proteins (Dnm1, Hpca, Stx1, Syn1, Syn2, Syp, SNAP25, VAMP2 and 14-3-3 eta, gamma, and zeta) were confirmed between Adult and Aged rats, with no further dysregulation associated with cognitive impairment. Proteins related to synaptic structural stability (MAP2, drebrin, Nogo-A) and activity-dependent signaling (PSD-95, 14-3-3θ, CaMKIIα) were up- and down-regulated, respectively, with cognitive impairment but were not altered with increasing age. Localization of MAP2, PSD-95, and CaMKIIα demonstrated protein expression alterations throughout the hippocampus. The altered expression of activity- and structural stability-associated proteins suggests that impaired synaptic plasticity is a distinct phenomenon that occurs with age-related cognitive decline, and demonstrates that cognitive decline is not simply an exacerbation of the aging phenotype.
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Affiliation(s)
- Heather D VanGuilder
- Penn State College of Medicine, Department of Pharmacology, Hershey Center for Applied Research, 500 University Drive, Hershey, PA 17033, USA
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112
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Mangin JM, Gallo V. The curious case of NG2 cells: transient trend or game changer? ASN Neuro 2011; 3:e00052. [PMID: 21288204 PMCID: PMC3052864 DOI: 10.1042/an20110001] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2010] [Accepted: 02/03/2011] [Indexed: 11/17/2022] Open
Abstract
It has been 10 years since the seminal work of Dwight Bergles and collaborators demonstrated that NG2 (nerve/glial antigen 2)-expressing oligodendrocyte progenitor cells (NG2 cells) receive functional glutamatergic synapses from neurons (Bergles et al., 2000), contradicting the old dogma that only neurons possess the complex and specialized molecular machinery necessary to receive synapses. While this surprising discovery may have been initially shunned as a novelty item of undefined functional significance, the study of neuron-to-NG2 cell neurotransmission has since become a very active and exciting field of research. Many laboratories have now confirmed and extended the initial discovery, showing for example that NG2 cells can also receive inhibitory GABAergic synapses (Lin and Bergles, 2004) or that neuron-to-NG2 cell synaptic transmission is a rather ubiquitous phenomenon that has been observed in all brain areas explored so far, including white matter tracts (Kukley et al., 2007; Ziskin et al., 2007; Etxeberria et al., 2010). Thus, while still being in its infancy, this field of research has already brought many surprising and interesting discoveries, and has become part of a continuously growing effort in neuroscience to re-evaluate the long underestimated role of glial cells in brain function (Barres, 2008). However, this area of research is now reaching an important milestone and its long-term significance will be defined by its ability to uncover the still elusive function of NG2 cells and their synapses in the brain, rather than by its sensational but transient successes at upsetting the old order established by neuronal physiology. To participate in the effort to facilitate such a transition, here we propose a critical review of the latest findings in the field of NG2 cell physiology--discussing how they inform us on the possible function(s) of NG2 cells in the brain--and we present some personal views on new directions the field could benefit from in order to achieve lasting significance.
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Key Words
- α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (ampar)
- nerve/glial antigen 2 (ng2) cells
- neuron
- oligodendrocyte progenitor cell (opc)
- postsynaptic density (psd)
- ampar, α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor
- cnp-gfp, c-type natriuretic peptide-green fluorescent protein
- cns, central nervous system
- egfp, enhanced green fluorescent protein
- epsc, excitatory postsynaptic current
- gaba, γ-aminobutyric acid
- gabaar, gaba type a receptor
- ltp, long-term potentiation
- mbp, maltose-binding protein
- ng2, nerve/glial antigen 2
- nmdar, n-methyl-d-aspartate receptor
- ol, oligodendrocyte lineage
- opc, oligodendrocyte progenitor cell
- pdgfrα, platelet-derived growth factor receptor α
- psd, postsynaptic density
- scp, schwann cell progenitor
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Affiliation(s)
- Jean-Marie Mangin
- Center for Neuroscience Research, Childrens National Medical Center, Washington, DC 20010, USA.
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113
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NogoA restricts synaptic plasticity in the adult hippocampus on a fast time scale. Proc Natl Acad Sci U S A 2011; 108:2569-74. [PMID: 21262805 DOI: 10.1073/pnas.1013322108] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Whereas the role of NogoA in limiting axonal fiber growth and regeneration following an injury of the mammalian central nervous system (CNS) is well known, its physiological functions in the mature uninjured CNS are less well characterized. NogoA is mainly expressed by oligodendrocytes, but also by subpopulations of neurons, in particular in plastic regions of the CNS, e.g., in the hippocampus where it is found at synaptic sites. We analyzed synaptic transmission as well as long-term synaptic plasticity (long-term potentiation, LTP) in the presence of function blocking anti-NogoA or anti-Nogo receptor (NgR) antibodies and in NogoA KO mice. Whereas baseline synaptic transmission, short-term plasticity and long-term depression were not affected by either approach, long-term potentiation was significantly increased following NogoA or NgR1 neutralization. Synaptic potentiation thus seems to be restricted by NogoA. Surprisingly, synaptic weakening was not affected by interfering with NogoA signaling. Mechanistically of interest is the observation that by blockade of the GABA(A) receptors normal synaptic strengthening reoccurred in the absence of NogoA signaling. The present results show a unique role of NogoA expressed in the adult hippocampus in restricting physiological synaptic plasticity on a very fast time scale. NogoA could thus serve as an important negative regulator of functional and structural plasticity in mature neuronal networks.
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114
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MHC class I modulates NMDA receptor function and AMPA receptor trafficking. Proc Natl Acad Sci U S A 2010; 107:22278-83. [PMID: 21135233 DOI: 10.1073/pnas.0914064107] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Proteins of the major histocompatibility complex class I (MHCI) are known for their role in immunity and have recently been implicated in long-term plasticity of excitatory synaptic transmission. However, the mechanisms by which MHCI influences synaptic plasticity remain unknown. Here we show that endogenous MHCI regulates synaptic responses mediated by NMDA-type glutamate receptors (NMDARs) in the mammalian central nervous system (CNS). The AMPA/NMDA ratio is decreased at MHCI-deficient hippocampal synapses, reflecting an increase in NMDAR-mediated currents. This enhanced NMDAR response is not associated with changes in the levels, subunit composition, or gross subcellular distribution of NMDARs. Increased NMDAR-mediated currents in MHCI-deficient neurons are associated with characteristic changes in AMPA receptor trafficking in response to NMDAR activation. Thus, endogenous MHCI tonically inhibits NMDAR function and controls downstream NMDAR-induced AMPA receptor trafficking during the expression of plasticity.
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