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Bin JM, Suminaite D, Benito-Kwiecinski SK, Kegel L, Rubio-Brotons M, Early JJ, Soong D, Livesey MR, Poole RJ, Lyons DA. Importin 13-dependent axon diameter growth regulates conduction speeds along myelinated CNS axons. Nat Commun 2024; 15:1790. [PMID: 38413580 PMCID: PMC10899189 DOI: 10.1038/s41467-024-45908-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 02/06/2024] [Indexed: 02/29/2024] Open
Abstract
Axon diameter influences the conduction properties of myelinated axons, both directly, and indirectly through effects on myelin. However, we have limited understanding of mechanisms controlling axon diameter growth in the central nervous system, preventing systematic dissection of how manipulating diameter affects myelination and conduction along individual axons. Here we establish zebrafish to study axon diameter. We find that importin 13b is required for axon diameter growth, but does not affect cell body size or axon length. Using neuron-specific ipo13b mutants, we assess how reduced axon diameter affects myelination and conduction, and find no changes to myelin thickness, precision of action potential propagation, or ability to sustain high frequency firing. However, increases in conduction speed that occur along single myelinated axons with development are tightly linked to their growth in diameter. This suggests that axon diameter growth is a major driver of increases in conduction speeds along myelinated axons over time.
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Affiliation(s)
- Jenea M Bin
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK.
| | - Daumante Suminaite
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | | | - Linde Kegel
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Maria Rubio-Brotons
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Jason J Early
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Daniel Soong
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Matthew R Livesey
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
- Sheffield Institute for Translational Neuroscience, University of Sheffield, Sheffield, S10 2HQ, UK
- Neuroscience Institute, University of Sheffield, Sheffield, S10 2TN, UK
| | - Richard J Poole
- Department of Cell and Developmental Biology, University College London, London, WC1E 6BT, UK
| | - David A Lyons
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK.
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Cha J, Filatov G, Smith SJ, Gammaitoni AR, Lothe A, Reeder T. Fenfluramine increases survival and reduces markers of neurodegeneration in a mouse model of Dravet syndrome. Epilepsia Open 2024; 9:300-313. [PMID: 38018342 PMCID: PMC10839300 DOI: 10.1002/epi4.12873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2023] [Accepted: 11/21/2023] [Indexed: 11/30/2023] Open
Abstract
OBJECTIVE In patients with Dravet syndrome (DS), fenfluramine reduced convulsive seizure frequency and provided clinical benefit in nonseizure endpoints (e.g., executive function, survival). In zebrafish mutant scn1 DS models, chronic fenfluramine treatment preserved neuronal cytoarchitecture prior to seizure onset and prevented gliosis; here, we extend these findings to a mammalian model of DS (Scn1a+/- mice) by evaluating the effects of fenfluramine on neuroinflammation (degenerated myelin, activated microglia) and survival. METHODS Scn1a+/- DS mice were treated subcutaneously once daily with fenfluramine (15 mg/kg) or vehicle from postnatal day (PND) 7 until 35-37. Sagittal brain sections were processed for immunohistochemistry using antibodies to degraded myelin basic protein (D-MBP) for degenerated myelin, or CD11b for activated (inflammatory) microglia; sections were scored semi-quantitatively. Apoptotic nuclei were quantified by TUNEL assay. Statistical significance was evaluated by 1-way ANOVA with post-hoc Dunnett's test (D-MBP, CD11b, and TUNEL) or Logrank Mantel-Cox (survival). RESULTS Quantitation of D-MBP immunostaining per 0.1 mm2 unit area of the parietal cortex and hippocampus CA3 yielded significantly higher spheroidal and punctate myelin debris counts in vehicle-treated DS mice than in wild-type mice. Fenfluramine treatment in DS mice significantly reduced these counts. Activated CD11b + microglia were more abundant in DS mouse corpus callosum and hippocampus than in wild-type controls. Fenfluramine treatment of DS mice resulted in significantly fewer activated CD11b + microglia than vehicle-treated DS mice in these brain regions. TUNEL staining in corpus callosum was increased in DS mice relative to wild-type controls. Fenfluramine treatment in DS mice lowered TUNEL staining relative to vehicle-treated DS mice. By PND 35-37, 55% of control DS mice had died, compared with 24% of DS mice receiving fenfluramine treatment (P = 0.0291). SIGNIFICANCE This is the first report of anti-neuroinflammation and pro-survival after fenfluramine treatment in a mammalian DS model. These results corroborate prior data in humans and animal models and suggest important pharmacological activities for fenfluramine beyond seizure reduction. PLAIN LANGUAGE SUMMARY Dravet syndrome is a severe epilepsy disorder that impairs learning and causes premature death. Clinical studies in patients with Dravet syndrome show that fenfluramine reduces convulsive seizures. Additional studies suggest that fenfluramine may have benefits beyond seizures, including promoting survival and improving control over emotions and behavior. Our study is the first to use a Dravet mouse model to investigate nonseizure outcomes of fenfluramine. Results showed that fenfluramine treatment of Dravet mice reduced neuroinflammation significantly more than saline treatment. Fenfluramine-treated Dravet mice also lived longer than saline-treated mice. These results support clinical observations that fenfluramine may have benefits beyond seizures.
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Affiliation(s)
- John Cha
- University of California San FranciscoSan FranciscoCaliforniaUSA
- Zogenix, Inc. (now a part of UCB)EmeryvilleCaliforniaUSA
| | - Gregory Filatov
- Zogenix, Inc. (now a part of UCB)EmeryvilleCaliforniaUSA
- Crosshair Therapeutics, Inc.SunnyvaleCaliforniaUSA
| | - Steven J. Smith
- Zogenix, Inc. (now a part of UCB)EmeryvilleCaliforniaUSA
- WuXi AppTec, Inc.San FranciscoCaliforniaUSA
| | | | | | - Thadd Reeder
- Zogenix, Inc. (now a part of UCB)EmeryvilleCaliforniaUSA
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Mito R, Pedersen M, Pardoe H, Parker D, Smith RE, Cameron J, Scheffer IE, Berkovic SF, Vaughan DN, Jackson GD. Exploring individual fixel-based white matter abnormalities in epilepsy. Brain Commun 2023; 6:fcad352. [PMID: 38187877 PMCID: PMC10768884 DOI: 10.1093/braincomms/fcad352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Revised: 11/02/2023] [Accepted: 12/21/2023] [Indexed: 01/09/2024] Open
Abstract
Diffusion MRI has provided insight into the widespread structural connectivity changes that characterize epilepsies. Although syndrome-specific white matter abnormalities have been demonstrated, studies to date have predominantly relied on statistical comparisons between patient and control groups. For diffusion MRI techniques to be of clinical value, they should be able to detect white matter microstructural changes in individual patients. In this study, we apply an individualized approach to a technique known as fixel-based analysis, to examine fibre-tract-specific abnormalities in individuals with epilepsy. We explore the potential clinical value of this individualized fixel-based approach in epilepsy patients with differing syndromic diagnoses. Diffusion MRI data from 90 neurologically healthy control participants and 10 patients with epilepsy (temporal lobe epilepsy, progressive myoclonus epilepsy, and Dravet Syndrome, malformations of cortical development) were included in this study. Measures of fibre density and cross-section were extracted for all participants across brain white matter fixels, and mean values were computed within select tracts-of-interest. Scanner harmonized and normalized data were then used to compute Z-scores for individual patients with epilepsy. White matter abnormalities were observed in distinct patterns in individual patients with epilepsy, both at the tract and fixel level. For patients with specific epilepsy syndromes, the detected white matter abnormalities were in line with expected syndrome-specific clinical phenotypes. In patients with lesional epilepsies (e.g. hippocampal sclerosis, periventricular nodular heterotopia, and bottom-of-sulcus dysplasia), white matter abnormalities were spatially concordant with lesion location. This proof-of-principle study demonstrates the clinical potential of translating advanced diffusion MRI methodology to individual-patient-level use in epilepsy. This technique could be useful both in aiding diagnosis of specific epilepsy syndromes, and in localizing structural abnormalities, and is readily amenable to other neurological disorders. We have included code and data for this study so that individualized white matter changes can be explored robustly in larger cohorts in future work.
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Affiliation(s)
- Remika Mito
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
- Florey Department of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria 3010, Australia
| | - Mangor Pedersen
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
- Department of Psychology and Neuroscience, Auckland University of Technology (AUT), Auckland 1142, New Zealand
| | - Heath Pardoe
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
| | - Donna Parker
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
| | - Robert E Smith
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
- Florey Department of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria 3010, Australia
| | - Jillian Cameron
- Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health, Heidelberg, Victoria 3084, Australia
| | - Ingrid E Scheffer
- Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health, Heidelberg, Victoria 3084, Australia
| | - Samuel F Berkovic
- Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health, Heidelberg, Victoria 3084, Australia
| | - David N Vaughan
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
- Florey Department of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria 3010, Australia
- Department of Neurology, Austin Health, Heidelberg, Victoria 3084, Australia
| | - Graeme D Jackson
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
- Florey Department of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria 3010, Australia
- Department of Neurology, Austin Health, Heidelberg, Victoria 3084, Australia
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Bortolami A, Sesti F. Ion channels in neurodevelopment: lessons from the Integrin-KCNB1 channel complex. Neural Regen Res 2023; 18:2365-2369. [PMID: 37282454 PMCID: PMC10360111 DOI: 10.4103/1673-5374.371347] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023] Open
Abstract
Ion channels modulate cellular excitability by regulating ionic fluxes across biological membranes. Pathogenic mutations in ion channel genes give rise to epileptic disorders that are among the most frequent neurological diseases affecting millions of individuals worldwide. Epilepsies are triggered by an imbalance between excitatory and inhibitory conductances. However, pathogenic mutations in the same allele can give rise to loss-of-function and/or gain-of-function variants, all able to trigger epilepsy. Furthermore, certain alleles are associated with brain malformations even in the absence of a clear electrical phenotype. This body of evidence argues that the underlying epileptogenic mechanisms of ion channels are more diverse than originally thought. Studies focusing on ion channels in prenatal cortical development have shed light on this apparent paradox. The picture that emerges is that ion channels play crucial roles in landmark neurodevelopmental processes, including neuronal migration, neurite outgrowth, and synapse formation. Thus, pathogenic channel mutants can not only cause epileptic disorders by altering excitability, but further, by inducing morphological and synaptic abnormalities that are initiated during neocortex formation and may persist into the adult brain.
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Affiliation(s)
- Alessandro Bortolami
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Rutgers University, West Piscataway, NJ, USA
| | - Federico Sesti
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Rutgers University, West Piscataway, NJ, USA
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Lenge M, Balestrini S, Mei D, Macconi L, Caligiuri ME, Cuccarini V, Aquino D, Mazzi F, d’Incerti L, Darra F, Bernardina BD, Guerrini R. Morphometry and network-based atrophy patterns in SCN1A-related Dravet syndrome. Cereb Cortex 2023; 33:9532-9541. [PMID: 37344172 PMCID: PMC10431750 DOI: 10.1093/cercor/bhad224] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 06/04/2023] [Accepted: 06/05/2023] [Indexed: 06/23/2023] Open
Abstract
Mutations of the voltage-gated sodium channel SCN1A gene (MIM#182389) are among the most clinically relevant epilepsy-related genetic mutations and present variable phenotypes, from the milder genetic epilepsy with febrile seizures plus to Dravet syndrome, a severe developmental and epileptic encephalopathy. Qualitative neuroimaging studies have identified malformations of cortical development in some patients and mild atrophic changes, partially confirmed by quantitative studies. Precise correlations between MRI findings and clinical variables have not been addressed. We used morphometric methods and network-based models to detect abnormal brain structural patterns in 34 patients with SCN1A-related epilepsy, including 22 with Dravet syndrome. By measuring the morphometric characteristics of the cortical mantle and volume of subcortical structures, we found bilateral atrophic changes in the hippocampus, amygdala, and the temporo-limbic cortex (P-value < 0.05). By correlating atrophic patterns with brain connectivity profiles, we found the region of the hippocampal formation as the epicenter of the structural changes. We also observed that Dravet syndrome was associated with more severe atrophy patterns with respect to the genetic epilepsy with febrile seizures plus phenotype (r = -0.0613, P-value = 0.03), thus suggesting that both the underlying mutation and seizure severity contribute to determine atrophic changes.
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Affiliation(s)
- Matteo Lenge
- Neuroscience Department, Meyer Children’s Hospital IRCCS, 50139, Florence, Italy
| | - Simona Balestrini
- Neuroscience Department, Meyer Children’s Hospital IRCCS, 50139, Florence, Italy
| | - Davide Mei
- Neuroscience Department, Meyer Children’s Hospital IRCCS, 50139, Florence, Italy
| | - Letizia Macconi
- Neuroradiology Unit, Meyer Children’s Hospital IRCCS, 50139, Florence, Italy
| | - Maria Eugenia Caligiuri
- Neuroscience Research Center, Department of Medical and Surgical Sciences, Magna Grecia University, 88100, Catanzaro, Italy
| | - Valeria Cuccarini
- Neuroradiology Unit, Fondazione IRCCS Neurologico Carlo Besta, 20100, Milan, Italy
| | - Domenico Aquino
- Neuroradiology Unit, Fondazione IRCCS Neurologico Carlo Besta, 20100, Milan, Italy
| | - Federica Mazzi
- Neuroradiology Unit, Fondazione IRCCS Neurologico Carlo Besta, 20100, Milan, Italy
| | - Ludovico d’Incerti
- Neuroradiology Unit, Meyer Children’s Hospital IRCCS, 50139, Florence, Italy
| | - Francesca Darra
- Child Neuropsychiatry Unit, Department of Engineering for Innovation Medicine University of Verona, 37100, Verona, Italy
| | - Bernardo Dalla Bernardina
- Child Neuropsychiatry Unit, Department of Engineering for Innovation Medicine University of Verona, 37100, Verona, Italy
- Pediatric Epilepsy Research Center (CREP), Azienda Ospedaliera Universitaria Integrata, 37100, Verona, Italy
| | - Renzo Guerrini
- Neuroscience Department, Meyer Children’s Hospital IRCCS, 50139, Florence, Italy
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