Neuroscience
Abstract
Focal cortical dysplasia (FCD) is a major cause of refractory epilepsy and is associated with pathogenic variants in mTOR pathway genes, including DEPDC5, the most common cause of familial focal epilepsy. The mechanisms of epileptogenesis associated with FCD and hyperactive mTOR signaling remain unclear in DEPDC5-related epilepsy. To test whether DEPDC5 loss leading to seizures require in utero cortical developmental defects or if postnatal neuronal dysfunction of mTORC1 is sufficient to drive seizures, we developed a postnatal focal cortical Depdc5 knockout mouse model. Postnatal day 0-1 Depdc5-floxed mice received unilateral motor cortex injections of either AAV-Cre-GFP or control AAV-GFP. The AAV-Cre-GFP injected hemisphere had decreased DEPDC5 levels with hyperactivation of mTOR that increased with age compared to both the contralateral hemisphere and the AAV-GFP injected mice. Cortical lamination was not disrupted by postnatal DEPDC5 loss. Pathologic hallmarks of FCDs were identified in the Depdc5 knockout hemisphere, including increased SMI-311 neurofilament staining, hypomyelination, astrogliosis, and microglial activation. Mice with postnatal cortical DEPDC5 loss exhibited lower seizure thresholds, increased focal seizures, and increased rates of seizure-induced death compared to control mice. This study demonstrates that postnatal DEPDC5 loss and subsequent mTOR hyperactivation without disruption of cortical migration is sufficient to cause epilepsy.
Authors
Karenna J. Groff, Yini Liang, Christopher Morici, Jinita Modasia, Leena Mehendale, Nishtha Gupta, Angelica D'Amore, Yongho Choe, Mustafa Q. Hameed, Alexander Rotenberg, Mustafa Sahin, Christopher J. Yuskaitis
Abstract
Wiedemann-Steiner syndrome (WDSTS) is a rare genetic cause of intellectual disability that is primarily caused by heterozygous loss of function variants in the gene encoding the histone lysine methyltransferase 2A (KMT2A). Prior studies have shown successful postnatal amelioration of disease phenotypes for Rett, Rubinstein-Taybi and Kabuki syndromes, which are related Mendelian disorders of the epigenetic machinery. To explore whether the neurological phenotype in WDSTS is treatable in-utero, we created a mouse model carrying a loss of function variant placed between two loxP sites. Kmt2a+/LSL mice demonstrated core features of WDSTS including growth retardation, craniofacial abnormalities, and hypertrichosis as well as hippocampal memory defects. The neurological phenotypes were rescued upon restoration of KMT2A in-utero following breeding to a nestin-Cre. Together, our data provided a mouse model to explore the potential therapeutic window in WDSTS. Our work suggested that WDSTS has a window of opportunity extending at least until the mid-point of in-utero development, making WDSTS an ideal candidate for future therapeutic strategies.
Authors
Tinna Reynisdottir, Kimberley J. Anderson, Katrin Möller, Stefán Pétursson, Andrew Brinn, Katheryn P. Franklin, Juan Ouyang, Asbjorg O. Snorradottir, Cathleen M. Lutz, Aamir R. Zuberi, Valerie B. DeLeon, Hans T. Bjornsson
Abstract
About one-third of neonatal seizures do not respond to the first-line anticonvulsant phenobarbital, which activates phasic inhibition and whose effectiveness decreases over time. Whether enhancing tonic inhibition can treat refractory seizures or status epilepticus in neonates remains uncertain. We evaluated the effect of recurrent seizure-like events (SLE) on α5- and δ-GABAAR subunit expression and tonic inhibition in neonatal C57BL/6J mice (P6-P9, both sexes) using acute brain slices. We investigated the impact of THIP (gaboxadol) on neonatal behavioral seizures, neuronal apoptosis, and neurodegeneration in vivo. We found neonatal neocortical expression of α5- and δ-GABAA receptor (GABAAR) subunits. Blocking α5-GABAARs with L-655,708 did not affect acute neonatal SLE, whereas enhancing δ-GABAARs with THDOC, a neurosteroid, reduced them. The α5- and δ-GABAAR membrane expression increased after 8 hours of neonatal SLE, and correlated with increased δ-mediated conductance, but not α5-mediated one. Enhancing tonic inhibition was more effective in reducing recurrent neonatal SLE (8 hours) compared to early treatment. Increasing tonic inhibition reduced the duration, severity, and number of kainic acid-induced in vivo neonatal behavioral seizures without increasing neurodegeneration or apoptosis. We conclude that recurrent neonatal seizures increase tonic inhibition. Therefore, enhancing tonic inhibition may be a treatment strategy for prolonged neonatal status epilepticus.
Authors
Gage T. Liddiard, Gordon F. Buchanan, Mark L. Schultz, Joseph Glykys
Abstract
Patients with Dravet syndrome (DS) present with severe, spontaneous seizures and ataxia. While most patients with DS have variants in the sodium channel Nav1.1 α subunit gene, SCN1A, variants in the sodium channel β1 subunit gene, SCN1B, are also linked to DS. Scn1b null mice model DS, with spontaneous generalized seizures that start in the second week of life. In Scn1b null cerebellum, neuronal pathfinding is severely altered, and Purkinje cells (PCs) and granule neurons have altered excitability. Here, we show that Scn1b null mice are ataxic. Expression of β1 protein in WT cerebellum, assessed using a CRISPR transgenic mouse model containing an in-frame V5 epitope tag at the β1 C-terminus, is widespread. Scn1b null PCs and interneurons in cerebellar slices have increased thresholds for action potential initiation and decreased repetitive firing frequency compared with WT. Scn1b null PCs have reduced transient and resurgent sodium current densities. We propose that reduced PC excitability underlies the ataxic phenotype of Scn1b mice. In addition, because cerebellar output to other areas of the brain can result in termination of seizures, we propose that PC hypoexcitability exacerbates the severe phenotype of this mouse model.
Authors
Yukun Yuan, Heather A. O’Malley, Jesse J. Winters, Alfonso Lavado, Nicholas S. Denomme, Shreeya Bakshi, Samantha L. Hodges, Luis Lopez-Santiago, Chunling Chen, Lori L. Isom
Abstract
Dravet syndrome (DS) is an early-onset epilepsy caused by loss of function mutations in the SCN1A gene, which encodes Nav1.1 channels that preferentially regulate activity of inhibitory neurons early in development. DS is associated with a high incidence of sudden unexpected death in epilepsy (SUDEP) by a mechanism that may involve respiratory failure. Evidence also shows that loss of Scn1a impaired activity of neurons in the retrotrapezoid nucleus (RTN) that regulate breathing in response to CO2/H+, suggesting breathing problems precede seizures and serve as a biomarker of SUDEP. Consistent with this, we showed that Scn1a+/- mice exhibited a blunted ventilatory response to CO2/H+ prior to overt seizure activity that worsened with disease progression. Later in development, some Scn1a+/- mice also showed a blunted ventilatory response to hypoxia. Importantly, the severity of respiratory problems correlated with mortality. We also found that pharmacological activation of Nav1.1 rescued activity deficits of RTN neurons in Scn1a+/- mice. We conclude that disordered breathing may be an early biomarker of SUDEP in DS, and at the cellular level loss of Scn1a disrupts RTN neurons by mechanisms involving disinhibition and pharmacological activation of Nav1.1 re-establish inhibitory control of RTN neurons and rescue activity deficits.
Authors
Brenda M, Milla, Eliandra Silva, Cleyton R. Sobrinho, Monica Strain, Daniel K. Mulkey
Abstract
Spinal muscular atrophy (SMA) is a neuromuscular disease caused by low levels of SMN protein. Several therapeutic approaches boosting SMN are approved for human patients, delivering remarkable improvements in lifespan and symptoms. However, emerging phenotypes, including neurodevelopmental comorbidities, are being reported in some treated SMA patients, indicative of alterations in brain development. Here, using a mouse model of severe SMA, we revealed an underlying neurodevelopmental phenotype in SMA where prenatal SMN-dependent defects in translation drove disruptions in non-motile primary cilia across the central nervous system (CNS). Low levels of SMN caused widespread perturbations in translation at embryonic day (E) 14.5 targeting genes associated with primary cilia. The density of primary cilia in vivo, as well as cilial length in vitro, was significantly decreased in prenatal SMA mice. Proteomic analysis revealed downstream perturbations in primary cilia-regulated signalling pathways, including Wnt signalling. Cell proliferation was concomitantly reduced in the hippocampus of SMA mice. Prenatal transplacental therapeutic intervention with SMN-restoring risdiplam rescued primary cilia defects in SMA mouse embryos. Thus, SMN protein is required for normal cellular and molecular development of primary cilia in the CNS. Early, systemic treatment with SMN-restoring therapies can successfully target neurodevelopmental comorbidities in SMA.
Authors
Federica Genovese, Yu-Ting Huang, Anna A.L. Motyl, Martina Paganin, Gaurav Sharma, Ilaria Signoria, Deborah Donzel, Nicole C.H. Lai, Marie Pronot, Rachel A. Kline, Helena Chaytow, Kimberley J. Morris, Kiterie M.E. Faller, Thomas M. Wishart, Ewout J.N. Groen, Michael A. Cousin, Gabriella Viero, Thomas H. Gillingwater
Abstract
Authors
Jayanta Mondal, Patrick Nylund, Prit Benny Malgulwar, William E. Johnson, Jason T. Huse
Abstract
Maternal low thyroxine (T4) serum levels during the first trimester of pregnancy correlate with cerebral cortex volume and mental development of the progeny, but why neural cells during early fetal brain development are vulnerable to maternal T4 levels remains unknown. In this study, using iPSCs obtained from a boy with a loss-of-function mutation in MCT8—a transporter previously identified as critical for thyroid hormone uptake and action in neural cells—we demonstrate that thyroid hormones induce transcriptional changes that promote the progression of human neural precursor cells along the dorsal projection trajectory. Consistent with these findings, single-cell, spatial, and bulk transcriptomics from MCT8-deficient cerebral organoids and cultures of human neural precursor cells underscore the necessity for optimal thyroid hormone levels for these cells to differentiate into neurons. The controlled intracellular activation of T4 signaling occurs through the transient expression of the enzyme type 2 deiodinase, which converts T4 into its active form, T3, alongside the coordinated expression of thyroid hormone nuclear receptors. The intracellular activation of T4 in NPCs results in transcriptional changes important for their division mode and cell cycle progression. Thus, T4 is essential for fetal neurogenesis, highlighting the importance of adequate treatment for mothers with hypothyroidism.
Authors
Federico Salas-Lucia, Sergio Escamilla, Amanda Charest, Hanzi Jiang, Randy Stout, Antonio C. Bianco
Abstract
Type I interferons (IFNs) are critical cytokines for antiviral defense and are linked to painful diseases like rheumatoid arthritis, lupus, and neuropathic pain in humans. IFN-α therapy can cause myalgia, headache, joint and abdominal pain. Studies in rodent models demonstrate that direct action of IFNs on sensory neurons in the dorsal root ganglion (DRG) promotes hyperexcitability but rodent behavioral data on IFNs are conflicting, with reports of both pro- and anti-nociceptive actions. We sought to clarify the action of IFN-α and IFN-β on human DRG (hDRG) nociceptors. We found that IFN receptor subunits IFNAR1 and IFNAR2 are expressed by these neurons and their engagement induces canonical STAT1 signaling and non-canonical MAPK activation as measured by increased phosphorylation of the cap-binding protein eIF4E by MNK1/2 kinases. Using patch clamp electrophysiology, Ca2+-imaging, and multi-electrode arrays we demonstrate that IFN-α and -β increase the excitability of hDRG neurons with acute and long-term exposure. Type I IFNs prolong the duration of capsaicin responses, an effect that is blocked by inhibition of MNK1/2 with eFT508, a specific inhibitor of these kinases. This study supports the conclusion that type I IFNs induce hyperexcitability and TRPV1-sensitization when they interact with IFNAR1/2 in hDRG nociceptors.
Authors
Úrzula Franco-Enzástiga, Keerthana Natarajan, Felipe Espinosa, Rafael Granja-Vazquez, Hemanth Mydugolam, Theodore J. Price
Abstract
Epilepsy is a common neurological disorder resulting from an imbalance between neuronal excitation and inhibition. Synapses play a pivotal role in the pathogenesis of epilepsy. Src-homology 2 (SH2) domain–containing protein 5 (SH2D5) is highly expressed in the brain and is implicated in the regulation of synaptic function. However, its role and mechanism in epilepsy remain unclear. In this study, we found that SH2D5 was predominantly localized to pyramidal neurons in the mouse hippocampus and was upregulated in the hippocampus of epileptic brains. KO of Sh2d5 in the hippocampus alleviated both the susceptibility to and severity of epileptic activity. Mechanistically, SH2D5 regulated N-methyl-D-aspartate receptor–mediated (NMDAR–mediated) excitatory synaptic transmission by altering the protein expression levels of NMDAR subunits. We further demonstrated that SH2D5 modulated the transcription of NMDARs by promoting the autophagic degradation of STAT1. These findings suggest that targeting the SH2D5/STAT1/NMDAR pathway may offer a potential therapeutic strategy for epilepsy.
Authors
Haokun Guo, Hui Zhang, Chenlu Zhang, Yuanyuan Shen, Liumi Jiang, Min Yang, Yuansong Zhang, Ningning Zhang, Ruirui Zhang, Ran Yu, Yong Yang, Xin Tian
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