1
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Adenosine A 2A receptors control synaptic remodeling in the adult brain. Sci Rep 2022; 12:14690. [PMID: 36038626 PMCID: PMC9424208 DOI: 10.1038/s41598-022-18884-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Accepted: 08/22/2022] [Indexed: 01/04/2023] Open
Abstract
The molecular mechanisms underlying circuit re-wiring in the mature brain remains ill-defined. An eloquent example of adult circuit remodelling is the hippocampal mossy fiber (MF) sprouting found in diseases such as temporal lobe epilepsy. The molecular determinants underlying this retrograde re-wiring remain unclear. This may involve signaling system(s) controlling axon specification/growth during neurodevelopment reactivated during epileptogenesis. Since adenosine A2A receptors (A2AR) control axon formation/outgrowth and synapse stabilization during development, we now examined the contribution of A2AR to MF sprouting. A2AR blockade significantly attenuated status epilepticus(SE)-induced MF sprouting in a rat pilocarpine model. This involves A2AR located in dentate granule cells since their knockdown selectively in dentate granule cells reduced MF sprouting, most likely through the ability of A2AR to induce the formation/outgrowth of abnormal secondary axons found in rat hippocampal neurons. These A2AR should be activated by extracellular ATP-derived adenosine since a similar prevention/attenuation of SE-induced hippocampal MF sprouting was observed in CD73 knockout mice. These findings demonstrate that A2AR contribute to epilepsy-related MF sprouting, most likely through the reactivation of the ability of A2AR to control axon formation/outgrowth observed during neurodevelopment. These results frame the CD73-A2AR axis as a regulator of circuit remodeling in the mature brain.
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2
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Mothe AJ, Jacobson PB, Caprelli M, Ulndreaj A, Rahemipour R, Huang L, Monnier PP, Fehlings MG, Tator CH. Delayed administration of elezanumab, a human anti-RGMa neutralizing monoclonal antibody, promotes recovery following cervical spinal cord injury. Neurobiol Dis 2022; 172:105812. [PMID: 35810963 DOI: 10.1016/j.nbd.2022.105812] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Revised: 07/03/2022] [Accepted: 07/04/2022] [Indexed: 11/19/2022] Open
Abstract
Spinal cord injury (SCI) elicits a cascade of degenerative events including cell death, axonal degeneration, and the upregulation of inhibitory molecules which limit repair. Repulsive guidance molecule A (RGMa) is an axon growth inhibitor which is also involved in neuronal cell death and differentiation. SCI causes upregulation of RGMa in the injured rodent, non-human primate, and human spinal cord. Recently, we showed that delayed administration of elezanumab, a high affinity human RGMa-specific monoclonal antibody, promoted neuroprotective and regenerative effects following thoracic SCI. Since most human traumatic SCI is at the cervical level, and level-dependent anatomical and molecular differences may influence pathophysiological responses to injury and treatment, we examined the efficacy of elezanumab and its therapeutic time window of administration in a clinically relevant rat model of cervical impact-compression SCI. Pharmacokinetic analysis of plasma and spinal cord tissue lysate showed comparable levels of RGMa antibodies with delayed administration following cervical SCI. At 12w after SCI, elezanumab promoted long term benefits including perilesional sparing of motoneurons and increased neuroplasticity of key descending pathways involved in locomotion and fine motor function. Elezanumab also promoted growth of corticospinal axons into spinal cord gray matter and enhanced serotonergic innervation of the ventral horn to form synaptic connections caudal to the cervical lesion. Significant recovery in grip and trunk/core strength, locomotion and gait, and spontaneous voiding ability was found in rats treated with elezanumab either immediately post-injury or at 3 h post-SCI, and improvements in specific gait parameters were found when elezanumab was delayed to 24 h post-injury. We also developed a new locomotor score, the Cervical Locomotor Score, a simple and sensitive measure of trunk/core and limb strength and stability during dynamic locomotion.
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Affiliation(s)
- Andrea J Mothe
- Division of Experimental and Translational Neuroscience, Krembil Brain Institute & University Health Network, Toronto, M5T 0S8, ON, Canada.
| | - Peer B Jacobson
- Department of Translational Sciences, AbbVie Inc., North Chicago, IL 60064, USA
| | - Mitchell Caprelli
- Division of Experimental and Translational Neuroscience, Krembil Brain Institute & University Health Network, Toronto, M5T 0S8, ON, Canada
| | - Antigona Ulndreaj
- Division of Experimental and Translational Neuroscience, Krembil Brain Institute & University Health Network, Toronto, M5T 0S8, ON, Canada
| | - Radmehr Rahemipour
- Division of Experimental and Translational Neuroscience, Krembil Brain Institute & University Health Network, Toronto, M5T 0S8, ON, Canada
| | - Lili Huang
- AbbVie Biologics, AbbVie Bioresearch Center, Worcester, MA 01605, USA
| | - Philippe P Monnier
- Division of Experimental and Translational Neuroscience, Krembil Brain Institute & University Health Network, Toronto, M5T 0S8, ON, Canada; Department of Ophthalmology and Vision Science, University of Toronto, Toronto, M5S 3H6, ON, Canada
| | - Michael G Fehlings
- Division of Experimental and Translational Neuroscience, Krembil Brain Institute & University Health Network, Toronto, M5T 0S8, ON, Canada; Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, M5T 2S8, ON, Canada
| | - Charles H Tator
- Division of Experimental and Translational Neuroscience, Krembil Brain Institute & University Health Network, Toronto, M5T 0S8, ON, Canada; Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, M5T 2S8, ON, Canada.
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3
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You J, Huang H, Chan CTY, Li L. Pathological Targets for Treating Temporal Lobe Epilepsy: Discoveries From Microscale to Macroscale. Front Neurol 2022; 12:779558. [PMID: 35069411 PMCID: PMC8777077 DOI: 10.3389/fneur.2021.779558] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2021] [Accepted: 11/30/2021] [Indexed: 12/15/2022] Open
Abstract
Temporal lobe epilepsy (TLE) is one of the most common and severe types of epilepsy, characterized by intractable, recurrent, and pharmacoresistant seizures. Histopathology of TLE is mostly investigated through observing hippocampal sclerosis (HS) in adults, which provides a robust means to analyze the related histopathological lesions. However, most pathological processes underlying the formation of these lesions remain elusive, as they are difficult to detect and observe. In recent years, significant efforts have been put in elucidating the pathophysiological pathways contributing to TLE epileptogenesis. In this review, we aimed to address the new and unrecognized neuropathological discoveries within the last 5 years, focusing on gene expression (miRNA and DNA methylation), neuronal peptides (neuropeptide Y), cellular metabolism (mitochondria and ion transport), cellular structure (microtubule and extracellular matrix), and tissue-level abnormalities (enlarged amygdala). Herein, we describe a range of biochemical mechanisms and their implication for epileptogenesis. Furthermore, we discuss their potential role as a target for TLE prevention and treatment. This review article summarizes the latest neuropathological discoveries at the molecular, cellular, and tissue levels involving both animal and patient studies, aiming to explore epileptogenesis and highlight new potential targets in the diagnosis and treatment of TLE.
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Affiliation(s)
- Jing You
- Department of Biomedical Engineering, University of North Texas, Denton, TX, United States
| | - Haiyan Huang
- Department of Nutrition and Food Science, Texas Women University, Denton, TX, United States
| | - Clement T Y Chan
- Department of Biomedical Engineering, University of North Texas, Denton, TX, United States
| | - Lin Li
- Department of Biomedical Engineering, University of North Texas, Denton, TX, United States.,Department of Neurology, University of California, Los Angeles, Los Angeles, CA, United States
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4
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Tsutsui K, Kim HS, Yoshikata C, Kimura K, Kubota Y, Shibata Y, Tian C, Liu J, Nishiwaki K. Repulsive guidance molecule acts in axon branching in Caenorhabditis elegans. Sci Rep 2021; 11:22370. [PMID: 34785759 PMCID: PMC8595726 DOI: 10.1038/s41598-021-01853-8] [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: 09/16/2021] [Accepted: 11/03/2021] [Indexed: 11/25/2022] Open
Abstract
Repulsive guidance molecules (RGMs) are evolutionarily conserved proteins implicated in repulsive axon guidance. Here we report the function of the Caenorhabditis elegans ortholog DRAG-1 in axon branching. The axons of hermaphrodite-specific neurons (HSNs) extend dorsal branches at the region abutting the vulval muscles. The drag-1 mutants exhibited defects in HSN axon branching in addition to a small body size phenotype. DRAG-1 expression in the hypodermal cells was required for the branching of the axons. Although DRAG-1 is normally expressed in the ventral hypodermis excepting the vulval region, its ectopic expression in vulval precursor cells was sufficient to induce the branching. The C-terminal glycosylphosphatidylinositol anchor of DRAG-1 was important for its function, suggesting that DRAG-1 should be anchored to the cell surface. Genetic analyses suggested that the membrane receptor UNC-40 acts in the same pathway with DRAG-1 in HSN branching. We propose that DRAG-1 expressed in the ventral hypodermis signals via the UNC-40 receptor expressed in HSNs to elicit branching activity of HSN axons.
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Affiliation(s)
- Kaname Tsutsui
- Department of Bioscience, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan
| | - Hon-Song Kim
- Department of Bioscience, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan
| | - Chizu Yoshikata
- Department of Bioscience, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan
| | - Kenji Kimura
- Department of Bioscience, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan
| | - Yukihiko Kubota
- Department of Bioscience, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan
| | - Yukimasa Shibata
- Department of Bioscience, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan
| | - Chenxi Tian
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Jun Liu
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Kiyoji Nishiwaki
- Department of Bioscience, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan.
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5
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Twible C, Abdo R, Zhang Q. Astrocyte Role in Temporal Lobe Epilepsy and Development of Mossy Fiber Sprouting. Front Cell Neurosci 2021; 15:725693. [PMID: 34658792 PMCID: PMC8514632 DOI: 10.3389/fncel.2021.725693] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 09/02/2021] [Indexed: 11/13/2022] Open
Abstract
Epilepsy affects approximately 50 million people worldwide, with 60% of adult epilepsies presenting an onset of focal origin. The most common focal epilepsy is temporal lobe epilepsy (TLE). The role of astrocytes in the presentation and development of TLE has been increasingly studied and discussed within the literature. The most common histopathological diagnosis of TLE is hippocampal sclerosis. Hippocampal sclerosis is characterized by neuronal cell loss within the Cornu ammonis and reactive astrogliosis. In some cases, mossy fiber sprouting may be observed. Mossy fiber sprouting has been controversial in its contribution to epileptogenesis in TLE patients, and the mechanisms surrounding the phenomenon have yet to be elucidated. Several studies have reported that mossy fiber sprouting has an almost certain co-existence with reactive astrogliosis within the hippocampus under epileptic conditions. Astrocytes are known to play an important role in the survival and axonal outgrowth of central and peripheral nervous system neurons, pointing to a potential role of astrocytes in TLE and associated cellular alterations. Herein, we review the recent developments surrounding the role of astrocytes in the pathogenic process of TLE and mossy fiber sprouting, with a focus on proposed signaling pathways and cellular mechanisms, histological observations, and clinical correlations in human patients.
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Affiliation(s)
- Carolyn Twible
- Department of Pathology and Lab Medicine, Western University, London, ON, Canada
| | - Rober Abdo
- Department of Pathology and Lab Medicine, Western University, London, ON, Canada.,Department of Anatomy and Cell Biology, Western University, London, ON, Canada
| | - Qi Zhang
- Department of Pathology and Lab Medicine, Western University, London, ON, Canada.,Department of Pathology and Lab Medicine, London Health Sciences Centre, University Hospital, London, ON, Canada
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6
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Andoh M, Ikegaya Y, Koyama R. Microglia modulate the structure and function of the hippocampus after early-life seizures. J Pharmacol Sci 2020; 144:212-217. [PMID: 33070840 DOI: 10.1016/j.jphs.2020.09.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 08/19/2020] [Accepted: 09/08/2020] [Indexed: 02/06/2023] Open
Abstract
The hippocampus is a brain region well-known to exhibit structural and functional changes in temporal lobe epilepsy. Studies analyzing the brains of patients with epilepsy and those from animal models of epilepsy have revealed that microglia are excessively activated, especially in the hippocampus. These findings suggest that microglia may contribute to the onset and aggravation of epilepsy; however, direct evidence for microglial involvement or the underlying mechanisms by which this occurs remain to be fully discovered. To date, neuron-microglia interactions have been vigorously studied in adult epilepsy models; such studies have clarified microglial responses to excessive synchronous firing of neurons. In contrast, the role of microglia in the postnatal brain of patients with epileptic seizures remain largely unclear. Some early-life seizures, such as complex febrile seizures, have been shown to cause structural and functional changes in the brain, which is a risk factor for future development of epilepsy. Because brain structure and function are actively modulated by microglia in both health and disease, it is essential to clarify the role of microglia in early-life seizures and its impact on epileptogenesis.
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Affiliation(s)
- Megumi Andoh
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Yuji Ikegaya
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Ryuta Koyama
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.
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7
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Feng Y, Duan C, Luo Z, Xiao W, Tian F. Silencing miR-20a-5p inhibits axonal growth and neuronal branching and prevents epileptogenesis through RGMa-RhoA-mediated synaptic plasticity. J Cell Mol Med 2020; 24:10573-10588. [PMID: 32779334 PMCID: PMC7521253 DOI: 10.1111/jcmm.15677] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 06/24/2020] [Accepted: 07/03/2020] [Indexed: 12/18/2022] Open
Abstract
Epileptogenesis is a potential process. Mossy fibre sprouting (MFS) and synaptic plasticity promote epileptogenesis. Overexpression of repulsive guidance molecule a (RGMa) prevents epileptogenesis by inhibiting MFS. However, other aspects underlying the RGMa regulatory process of epileptogenesis have not been elucidated. We studied whether RGMa could be modulated by microRNAs and regulated RhoA in epileptogenesis. Using microRNA databases, we selected four miRNAs as potential candidates. We further experimentally confirmed miR‐20a‐5p as a RGMa upstream regulator. Then, in vitro, by manipulating miR‐20a‐5p and RGMa, we investigated the regulatory relationship between miR‐20a‐5p, RGMa and RhoA, and the effects of this pathway on neuronal morphology. Finally, in the epilepsy animal model, we determined whether the miR‐20a‐5p‐RGMa‐RhoA pathway influenced MFS and synaptic plasticity and then modified epileptogenesis. Our results showed that miR‐20a‐5p regulated RGMa and that RGMa regulated RhoA in vitro. Furthermore, in primary hippocampal neurons, the miR‐20a‐5p‐RGMa‐RhoA pathway regulated axonal growth and neuronal branching; in the PTZ‐induced epilepsy model, silencing miR‐20a‐5p prevented epileptogenesis through RGMa‐RhoA‐mediated synaptic plasticity but did not change MFS. Overall, we concluded that silencing miR‐20a‐5p inhibits axonal growth and neuronal branching and prevents epileptogenesis through RGMa‐RhoA‐mediated synaptic plasticity in the PTZ‐induced epilepsy model, thereby providing a possible strategy to prevent epileptogenesis.
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Affiliation(s)
- Yanyan Feng
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
| | - Chaojun Duan
- Department of Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Zhaohui Luo
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
| | - Wenbiao Xiao
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
| | - Fafa Tian
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
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8
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Song M, Tian F, Xia H, Xie Y. Repulsive guidance molecule a suppresses seizures and mossy fiber sprouting via the FAK‑p120RasGAP‑Ras signaling pathway. Mol Med Rep 2019; 19:3255-3262. [PMID: 30816469 DOI: 10.3892/mmr.2019.9951] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 01/21/2019] [Indexed: 11/05/2022] Open
Abstract
Repulsive guidance molecule a (RGMa) is a membrane‑associated glycoprotein that regulates axonal guidance and inhibits axon outgrowth. In our previous study, we hypothesized that RGMa may be involved in temporal lobe epilepsy (TLE) via the repulsive guidance molecule a (RGMa)‑focal adhesion kinase (FAK)‑Ras signaling pathway. To investigate the role of RGMa in epilepsy, recombinant RGMa protein and FAK inhibitor 14 was intracerebroventricularly injected into a pentylenetetrazol (PTZ) kindling model and Timm staining, co‑immunoprecipitation and western blotting analyses were subsequently performed. The results of the present study revealed that intracerebroventricular injection of recombinant RGMa protein reduced the phosphorylation of FAK (Tyr397) and intracerebroventricular injection of FAK inhibitor 14 reduced the interaction between FAK and p120GAP, as wells as Ras expression. Recombinant RGMa protein and FAK inhibitor 14 exerted seizure‑suppressant effects; however, recombinant RGMa protein but not FAK inhibitor 14 suppressed mossy fiber sprouting in the PTZ kindling model. Collectively, these results demonstrated that RGMa may be considered as a potential therapeutic agent for epilepsy, and that RGMa may exert the aforementioned biological effects partly via the FAK‑p120GAP‑Ras signaling pathway.
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Affiliation(s)
- Mingyu Song
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
| | - Fafa Tian
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
| | - Huang Xia
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
| | - Yuanyuan Xie
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
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9
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Cavarsan CF, Malheiros J, Hamani C, Najm I, Covolan L. Is Mossy Fiber Sprouting a Potential Therapeutic Target for Epilepsy? Front Neurol 2018; 9:1023. [PMID: 30555406 PMCID: PMC6284045 DOI: 10.3389/fneur.2018.01023] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 11/13/2018] [Indexed: 11/13/2022] Open
Abstract
Mesial temporal lobe epilepsy (MTLE) caused by hippocampal sclerosis is one of the most frequent focal epilepsies in adults. It is characterized by focal seizures that begin in the hippocampus, sometimes spread to the insulo-perisylvian regions and may progress to secondary generalized seizures. Morphological alterations in hippocampal sclerosis are well defined. Among them, hippocampal sclerosis is characterized by prominent cell loss in the hilus and CA1, and abnormal mossy fiber sprouting (granular cell axons) into the dentate gyrus inner molecular layer. In this review, we highlight the role of mossy fiber sprouting in seizure generation and hippocampal excitability and discuss the response of alternative treatment strategies in terms of MFS and spontaneous recurrent seizures in models of TLE (temporal lobe epilepsy).
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Affiliation(s)
- Clarissa F Cavarsan
- Department of Physiology, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Jackeline Malheiros
- Department of Physiology, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Clement Hamani
- Department of Physiology, Universidade Federal de São Paulo, São Paulo, Brazil.,Harquail Centre for Neuromodulation, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada
| | - Imad Najm
- Epilepsy Center, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Luciene Covolan
- Department of Physiology, Universidade Federal de São Paulo, São Paulo, Brazil.,Epilepsy Center, Neurological Institute, Cleveland Clinic, Cleveland, OH, United States
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10
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Oliveira ADAB, Melo NDFM, Vieira ÉDS, Nogueira PAS, Coope A, Velloso LA, Dezonne RS, Ueira-Vieira C, Botelho FV, Gomes JDAS, Zanon RG. Palmitate treated-astrocyte conditioned medium contains increased glutathione and interferes in hypothalamic synaptic network in vitro. Neurochem Int 2018; 120:140-148. [DOI: 10.1016/j.neuint.2018.08.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2018] [Revised: 07/30/2018] [Accepted: 08/16/2018] [Indexed: 01/03/2023]
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11
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Koyama R, Ikegaya Y. The Molecular and Cellular Mechanisms of Axon Guidance in Mossy Fiber Sprouting. Front Neurol 2018; 9:382. [PMID: 29896153 PMCID: PMC5986954 DOI: 10.3389/fneur.2018.00382] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 05/11/2018] [Indexed: 01/25/2023] Open
Abstract
The question of whether mossy fiber sprouting is epileptogenic has not been resolved; both sprouting-induced recurrent excitatory and inhibitory circuit hypotheses have been experimentally (but not fully) supported. Therefore, whether mossy fiber sprouting is a potential therapeutic target for epilepsy remains under debate. Moreover, the axon guidance mechanisms of mossy fiber sprouting have attracted the interest of neuroscientists. Sprouting of mossy fibers exhibits several uncommon axonal growth features in the basically non-plastic adult brain. For example, robust branching of axonal collaterals arises from pre-existing primary mossy fiber axons. Understanding the branching mechanisms in adulthood may contribute to axonal regeneration therapies in neuroregenerative medicine in which robust axonal re-growth is essential. Additionally, because granule cells are produced throughout life in the neurogenic dentate gyrus, it is interesting to examine whether the mossy fibers of newly generated granule cells follow the pre-existing trajectories of sprouted mossy fibers in the epileptic brain. Understanding these axon guidance mechanisms may contribute to neuron transplantation therapies, for which the incorporation of transplanted neurons into pre-existing neural circuits is essential. Thus, clarifying the axon guidance mechanisms of mossy fiber sprouting could lead to an understanding of central nervous system (CNS) network reorganization and plasticity. Here, we review the molecular and cellular mechanisms of axon guidance in mossy fiber sprouting by discussing mainly in vitro studies.
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Affiliation(s)
- Ryuta Koyama
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Yuji Ikegaya
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
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12
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Abstract
Epileptogenesis, which can be initiated by brain insults or gene mutations in the normal brain, is defined as the gradual (months to years) process of epilepsy development that begins before the first epileptic seizure. Epileptogenic changes include induction of immediate early genes, post-translational modification of ion-channel functions, neuronal death, gliosis, and reorganization of neural circuits. Each of these changes alone or in combination can contribute to an epileptogenic focus, which is defined by the minimal cortical region that is necessary and sufficient to induce synchronized epileptic bursting activity in neurons. Therefore to discover and develop anti-epileptogenic drugs it is essential to unveil the cellular and molecular mechanisms underlying the development of epileptogenic foci. Among the epileptogenic changes, abnormally appended excitatory recurrent circuits can directly cause synchronized bursting of neuron activity. Here, I will introduce and discuss the mechanisms underlying the development of two representative abnormal neural circuits, namely, hippocampal mossy fiber sprouting and ectopic granule cells, which are found in the dentate gyrus of patients with mesial temporal lobe epilepsy and its animal models.
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Affiliation(s)
- Ryuta Koyama
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo
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13
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Lentiviral Vector-Induced Overexpression of RGMa in the Hippocampus Suppresses Seizures and Mossy Fiber Sprouting. Mol Neurobiol 2016; 54:1379-1391. [PMID: 26843113 DOI: 10.1007/s12035-016-9744-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 01/22/2016] [Indexed: 10/22/2022]
Abstract
Repulsive guidance molecule a (RGMa) is a membrane-bound protein that inhibits axon outgrowth in the central nervous system. Temporal lobe epilepsy (TLE) is a common neurological disorder characterized by recurrent spontaneous seizures. To explore the role of RGMa in epilepsy, we investigated the expression of RGMa in patients with TLE, pilocarpine-induced rat model, and pentylenetetrazol kindling model of epilepsy, and then we performed behavioral, histological, and electrophysiological analysis by lentivirus-mediated overexpression of RGMa in the hippocampus of animal model. We found that RGMa was significantly decreased in TLE patients and in experimental rats from 6 h to 60 days after pilocarpine-induced seizures. In two types of epileptic animal models, pilocarpine-induced model and pentylenetetrazol kindling model, overexpression of RGMa in the hippocampus of rats exerted seizure-suppressant effects. The reduced spontaneous seizures were accompanied by attenuation of hippocampal mossy fiber sprouting. In addition, overexpression of RGMa inhibited hyperexcitability of hippocampal neurons via suppressing NMDAR-mediated currents in Mg2+-free-induced organotypic slice model. Collectively, these results demonstrate that overexpression of RGMa could be an alternative strategy for epilepsy therapy.
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