Roles of KChIP1 in the regulation of GABA-mediated transmission and behavioral anxiety

AAV-Mediated CAG-Targeting Selectively Reduces Polyglutamine-Expanded Protein and Attenuates Disease Phenotypes in a Spinocerebellar Ataxia Mouse Model

Polyglutamine (polyQ)-encoding CAG repeat expansions represent a common disease-causing mutation responsible for several dominant spinocerebellar ataxias (SCAs). PolyQ-expanded SCA proteins are toxic for cerebellar neurons, with Purkinje cells (PCs) being the most vulnerable. RNA interference (RNAi) reagents targeting transcripts with expanded CAG reduce the level of various mutant SCA proteins in an allele-selective manner in vitro and represent promising universal tools for treating multiple CAG/polyQ SCAs. However, it remains unclear whether the therapeutic targeting of CAG expansion can be achieved in vivo and if it can ameliorate cerebellar functions. Here, using a mouse model of SCA7 expressing a mutant Atxn7 allele with 140 CAGs, we examined the efficacy of short hairpin RNAs (shRNAs) targeting CAG repeats expressed from PHP.eB adeno-associated virus vectors (AAVs), which were introduced into the brain via intravascular injection. We demonstrated that shRNAs carrying various mismatches with the CAG target sequence reduced the level of polyQ-expanded ATXN7 in the cerebellum, albeit with varying degrees of allele selectivity and safety profile. An shRNA named A4 potently reduced the level of polyQ-expanded ATXN7, with no effect on normal ATXN7 levels and no adverse side effects. Furthermore, A4 shRNA treatment improved a range of motor and behavioral parameters 23 weeks after AAV injection and attenuated the disease burden of PCs by preventing the downregulation of several PC-type-specific genes. Our results show the feasibility of the selective targeting of CAG expansion in the cerebellum using a blood-brain barrier-permeable vector to attenuate the disease phenotype in an SCA mouse model. Our study represents a significant advancement in developing CAG-targeting strategies as a potential therapy for SCA7 and possibly other CAG/polyQ SCAs.

Characterization of a loss-of-function NSF attachment protein beta mutation in monozygotic triplets affected with epilepsy and autism using cortical neurons from proband-derived and CRISPR-corrected induced pluripotent stem cell lines

We investigated whether a homozygous recessive genetic variant of NSF attachment protein beta (NAPB) gene inherited by monozygotic triplets contributed to their phenotype of early-onset epilepsy and autism. Induced pluripotent stem cell (iPSC) lines were generated from all three probands and both parents. The NAPB genetic variation was corrected in iPSC lines from two probands by CRISPR/Cas9 gene editing. Cortical neurons were produced by directed, in vitro differentiation from all iPSC lines. These cell line-derived neurons enabled us to determine that the genetic variation in the probands causes exon skipping and complete absence of NAPB protein. Electrophysiological and transcriptomic comparisons of cortical neurons derived from parents and probands cell lines indicate that loss of NAPB function contributes to alterations in neuronal functions and likely contributed to the impaired neurodevelopment of the triplets.

Cellular plasticity and myeloid inflammation in the adult brain are independent of the transcriptional modulator DREAM

The downstream regulatory element antagonist modulator (DREAM) modulates ion channel function and gene transcription. Functionally, DREAM is implicated in physiological and pathological processes including cell proliferation, inflammation, and nociception. Despite its multiple functions and robust expression in forebrain tissue, neurons and glial cells, the role of DREAM in regard to cellular plasticity and tumor necrosis factor (TNF)-mediated inflammation is largely unexplored. Here, we demonstrate that adult hippocampal neurogenesis as well as the density and plasticity of glial cells in the hippocampus and thalamus are independent of the presence of DREAM. Further, DREAM deletion does not alter the regional myeloid response and inflammatory gene expression induced by chronic peripheral inflammation in mice overexpressing human TNF. Our data suggest that despite their highly dynamic regulation, neural cell plasticity and adult neurogenesis in the hippocampus do not depend on the multifunctional protein DREAM. Furthermore, TNF-mediated myeloid inflammation in the brain persists in the absence of DREAM.

Ahmed E, Baldassari S, Achaz G, Elmugadam FA, Abdelgadir WA, Baulac S, Buratti J, Abdalla O, Gamil S, Alzubeir M, Abubaker R, Noé E, Elsayed L, Ahmed AE, Leguern E. Involvement of ADGRV1 Gene in Familial Forms of Genetic Generalized Epilepsy

Background: Genetic generalized epilepsies (GGE) including childhood absence epilepsy (CAE), juvenile absence epilepsy (JAE), juvenile myoclonic epilepsy (JME), and GGE with tonic-clonic seizures alone (GGE-TCS), are common types of epilepsy mostly determined by a polygenic mode of inheritance. Recent studies showed that susceptibility genes for GGE are numerous, and their variants rare, challenging their identification. In this study, we aimed to assess GGE genetic etiology in a Sudanese population. Methods: We performed whole-exome sequencing (WES) on DNA of 40 patients from 20 Sudanese families with GGE searching for candidate susceptibility variants, which were prioritized by CADD software and functional features of the corresponding gene. We assessed their segregation in 138 individuals and performed genotype-phenotype correlations. Results: In a family including three sibs with GGE-TCS, we identified a rare missense variant in ADGRV1 encoding an adhesion G protein-coupled receptor V1, which was already involved in the autosomal recessive Usher type C syndrome. In addition, five other ADGRV1 rare missense variants were identified in four additional families and absent from 119 Sudanese controls. In one of these families, an ADGRV1 variant was found at a homozygous state, in a female more severely affected than her heterozygous brother, suggesting a gene dosage effect. In the five families, GGE phenotype was statistically associated with ADGRV1 variants (0R = 0.9 103). Conclusion: This study highly supports, for the first time, the involvement of ADGRV1 missense variants in familial GGE and that ADGRV1 is a susceptibility gene for CAE/JAE and GGE-TCS phenotypes.

Cellular and Subcellular Localisation of Kv4-Associated KChIP Proteins in the Rat Cerebellum

The K⁺ channel interacting proteins (KChIPs) are a family of cytosolic proteins that interact with Kv4 channels, leading to higher current density, modulation of channel inactivation and faster recovery from inactivation. Using immunohistochemical techniques at the light and electron microscopic level combined with quantitative analysis, we investigated the cellular and subcellular localisation of KChIP3 and KChIP4 to compare their distribution patterns with those for Kv4.2 and Kv4.3 in the cerebellar cortex. Immunohistochemistry at the light microscopic level demonstrated that KChIP3, KChIP4, Kv4.2 and Kv4.3 proteins were widely expressed in the cerebellum, with mostly overlapping patterns. Immunoelectron microscopic techniques showed that KChIP3, KChIP4, Kv4.2 and Kv4.3 shared virtually the same somato-dendritic domains of Purkinje cells and granule cells. Application of quantitative approaches showed that KChIP3 and KChIP4 were mainly membrane-associated, but also present at cytoplasmic sites close to the plasma membrane, in dendritic spines and shafts of Purkinje cells (PCs) and dendrites of granule cells (GCs). Similarly, immunoparticles for Kv4.2 and Kv4.3 were observed along the plasma membrane and at intracellular sites in the same neuron populations. In addition to the preferential postsynaptic distribution, KChIPs and Kv4 were also distributed presynaptically in parallel fibres and mossy fibres. Immunoparticles for KChIP3, KChIP4 and Kv4.3 were detected in parallel fibres, and KChIP3, KChIP4, Kv4.2 and Kv4.3 were found in parallel fibres, indicating that composition of KChIP and Kv4 seems to be input-dependent. Together, our findings unravelled previously uncharacterised KChIP and Kv4 subcellular localisation patterns in neurons, revealed that KChIP have additional Kv4-unrelated functions in the cerebellum and support the formation of macromolecular complexes between KChIP3 and KChIP4 with heterotetrameric Kv4.2/Kv4.3 channels.

Use of human neuroblastoma SH-SY5Y cells to evaluate glyphosate-induced effects on oxidative stress, neuronal development and cell death signaling pathways

Glyphosate-containing herbicides are the most used agrochemicals in the world. Their indiscriminate application raises some concerns regarding the possible health and environmental hazards. In this study, we investigated in human neuroblastoma cell line SH-SY5Y if oxidative stress, altered neurodevelopment and cell death pathways are involved in response to glyphosate and its metabolite aminomethylphosphonic acid (AMPA) exposures. MTT and LDH assays were carried out to assess the glyphosate and AMPA cytotoxicity. Lipid peroxides measured as malondialdehyde (MDA), nitric oxide (NO) and reactive oxygen species (ROS) production, and caspase-Glo 3/7 activity were evaluated. The neuroprotective role of melatonin (MEL), Trolox, N-acetylcysteine (NAC) and Sylibin against glyphosate- and AMPA-induced oxidative stress was examined. Glyphosate and AMPA effects on neuronal development related gene transcriptions, and gene expression profiling of cell death pathways by Real-Time PCR array were also investigated. Glyphosate (5 mM) and AMPA (10 mM) induced a significant increase in MDA levels, NO and ROS production and caspase 3/7 activity. Glyphosate exposure induced up-regulation of Wnt3a, Wnt5a, Wnt7a, CAMK2A, CAMK2B and down-regulation of GAP43 and TUBB3 mRNA expression involved in normal neural cell development. In relation to gene expression profiling of cell death pathways, of the 84 genes examined in cells a greater than 2-fold change was observed for APAF1, BAX, BCL2, CASP3, CASP7, CASP9, SYCP2, TNF, TP53, CTSB, NFκB1, PIK3C3, SNCA, SQSTMT, HSPBAP1 and KCNIPI mRNA expression for glyphosate and AMPA exposures. These gene expression data can help to define neurotoxic mechanisms of glyphosate and AMPA. Our results demonstrated that glyphosate and AMPA induced cytotoxic effects on neuronal development, oxidative stress and cell death via apoptotic, autophagy and necrotic pathways and confirmed that glyphosate environmental exposure becomes a concern. This study demonstrates that SH-SY5Y cell line could be considered an in vitro system for pesticide screening.

Calcium Sensors in Neuronal Function and Dysfunction

Calcium signaling in neurons as in other cell types can lead to varied changes in cellular function. Neuronal Ca²⁺ signaling processes have also become adapted to modulate the function of specific pathways over a wide variety of time domains and these can have effects on, for example, axon outgrowth, neuronal survival, and changes in synaptic strength. Ca²⁺ also plays a key role in synapses as the trigger for fast neurotransmitter release. Given its physiological importance, abnormalities in neuronal Ca²⁺ signaling potentially underlie many different neurological and neurodegenerative diseases. The mechanisms by which changes in intracellular Ca²⁺ concentration in neurons can bring about diverse responses is underpinned by the roles of ubiquitous or specialized neuronal Ca²⁺ sensors. It has been established that synaptotagmins have key functions in neurotransmitter release, and, in addition to calmodulin, other families of EF-hand-containing neuronal Ca²⁺ sensors, including the neuronal calcium sensor (NCS) and the calcium-binding protein (CaBP) families, play important physiological roles in neuronal Ca²⁺ signaling. It has become increasingly apparent that these various Ca²⁺ sensors may also be crucial for aspects of neuronal dysfunction and disease either indirectly or directly as a direct consequence of genetic variation or mutations. An understanding of the molecular basis for the regulation of the targets of the Ca²⁺ sensors and the physiological roles of each protein in identified neurons may contribute to future approaches to the development of treatments for a variety of human neuronal disorders.

Attention-deficit/hyperactivity disorder associated with KChIP1 rs1541665 in Kv channels accessory proteins

Attention-deficit/hyperactivity disorder (ADHD) is an early onset childhood neurodevelopmental disorder with high heritability. A number of genetic risk factors and environment factors have been implicated in the pathogenesis of ADHD. Genes encoding for subtypes of voltage-dependent K channels (Kv) and accessory proteins to these channels have been identified in genome-wide association studies (GWAS) of ADHD. We conducted a two-stage case–control study to investigate the associations between five key genes (KChIP4, KChIP1, DPP10, FHIT, and KCNC1) and the risk of developing ADHD. In the discovery stage comprising 256 cases and 372 controls, KChIP1 rs1541665 and FHIT rs3772475 were identified; they were further genotyped in the validation stage containing 328cases and 431 controls.KChIP1 rs1541665 showed significant association with a risk of ADHD at both stages, with CC vs TT odds ratio (OR) = 1.961, 95% confidence interval (CI) = 1.366–2.497, in combined analyses (P-FDR = 0.007). Moreover, we also found rs1541665 involvement in ADHD-I subtype (OR (95% CI) = 2.341(1.713, 3.282), and Hyperactive index score (P = 0.005) in combined samples.Intriguingly, gene-environmental interactions analysis consistently revealed the potential interactionsof rs1541665 collaboratingwith maternal stress pregnancy (P_mul = 0.021) and blood lead (P_add = 0.017) to modify ADHD risk. In conclusion, the current study provides evidence that genetic variants of Kv accessory proteins may contribute to the susceptibility of ADHD.Further studies with different ethnicitiesare warranted to produce definitive conclusions.

The long non-coding RNA NEAT1 is responsive to neuronal activity and is associated with hyperexcitability states

Despite their abundance, the molecular functions of long non-coding RNAs in mammalian nervous systems remain poorly understood. Here we show that the long non-coding RNA, NEAT1, directly modulates neuronal excitability and is associated with pathological seizure states. Specifically, NEAT1 is dynamically regulated by neuronal activity in vitro and in vivo, binds epilepsy-associated potassium channel-interacting proteins including KCNAB2 and KCNIP1, and induces a neuronal hyper-potentiation phenotype in iPSC-derived human cortical neurons following antisense oligonucleotide knockdown. Next generation sequencing reveals a strong association of NEAT1 with increased ion channel gene expression upon activation of iPSC-derived neurons following NEAT1 knockdown. Furthermore, we show that while NEAT1 is acutely down-regulated in response to neuronal activity, repeated stimulation results in NEAT1 becoming chronically unresponsive in independent in vivo rat model systems relevant to temporal lobe epilepsy. We extended previous studies showing increased NEAT1 expression in resected cortical tissue from high spiking regions of patients suffering from intractable seizures. Our results indicate a role for NEAT1 in modulating human neuronal activity and suggest a novel mechanistic link between an activity-dependent long non-coding RNA and epilepsy.

Neuroprotective or neurotoxic effects of 4-aminopyridine mediated by KChIP1 regulation through adjustment of Kv 4.3 potassium channels expression and GABA-mediated transmission in primary hippocampal cells

4-Aminopyridine (4-AP) is a potassium channel blocker used for the treatment of neuromuscular disorders. Otherwise, it has been described to produce a large number of adverse effects among them cell death mediated mainly by blockage of K(+) channels. However, a protective effect against cell death has also been described. On the other hand, Kv channel interacting protein 1 (KChIP1) is a neuronal calcium sensor protein that is predominantly expressed at GABAergic synapses and it has been related with modulation of K(+) channels, GABAergic transmission and cell death. According to this KChIP1 could play a key role in the protective or toxic effects induced by 4-AP. We evaluated, in wild type and KChIP1 silenced primary hippocampal neurons, the effect of 4-AP (0.25μM to 2mM) with or without semicarbazide (0.3M) co-treatment after 24h and after 14 days 4-AP alone exposure on cell viability, the effect of 4-AP (0.25μM to 2mM) on KChIP1 and Kv 4.3 potassium channels gene expression and GABAergic transmission after 24h treatment or after 14 days exposure to 4-AP (0.25μM to1μM). 4-AP induced cell death after 24h (from 1mM) and after 14 days treatment. We observed that 4-AP modulates KChIP1 which regulate Kv 4.3 channels expression and GABAergic transmission. Our study suggests that KChIP1 is a key gene that has a protective effect up to certain concentration after short-term treatment with 4-AP against induced cell injury; but this protection is erased after long term exposure, due to KChIP1 down-regulation predisposing cell to 4-AP induced damages. These data might help to explain protective and toxic effects observed after overdose and long term exposure.

Protein kinase C is essential for kainate-induced anxiety-related behavior and glutamatergic synapse upregulation in prelimbic cortex

AIM

Anxiety is one of common mood disorders, in which the deficit of serotonergic and GABAergic synaptic functions in the amygdala and prefrontal cortex is believed to be involved. The pathological changes at the glutamatergic synapses and neurons in these brain regions as well as their underlying mechanisms remain elusive, which we aim to investigate.

METHODS

An agonist of kainate-type glutamate receptors, kainic acid, was applied to induce anxiety-related behaviors. The morphology and functions of glutamatergic synapses in the prelimbic region of mouse prefrontal cortex were analyzed using cellular imaging and electrophysiology.

RESULTS

After kainate-induced anxiety is onset, the signal transmission at the glutamatergic synapses is upregulated, and the dendritic spine heads are enlarged. In terms of the molecular mechanisms, the upregulated synaptic plasticity is associated with the expression of more protein kinase C (PKC) in the dendritic spines. Chelerythrine, a PKC inhibitor, reverses kainate-induced anxiety and anxiety-related glutamatergic synapse upregulation.

CONCLUSION

The activation of glutamatergic kainate-type receptors leads to anxiety-related behaviors and glutamatergic synapse upregulation through protein kinase C in the prelimbic region of the mouse prefrontal cortex.

GCY-8, PDE-2, and NCS-1 are critical elements of the cGMP-dependent thermotransduction cascade in the AFD neurons responsible for C. elegans thermotaxis

Certain thermoreceptor neurons are sensitive to tiny thermal fluctuations (0.01°C or less) and maintain their sensitivity across a wide range of ambient temperatures through a process of adaptation, but understanding of the biochemical basis for this performance is rudimentary. Prior studies of the AFD thermoreceptor in Caenorhabditis elegans revealed a signaling cascade that depends on a trio of receptor guanylate cyclases (rGCs), GCY-8, GCY-18, and GCY-23, and gives rise to warming-activated thermoreceptor currents (ThRCs) carried by cyclic GMP–gated ion channels. The threshold for ThRC activation adapts to the ambient temperature through an unknown calcium-dependent process. Here, we use in vivo whole-cell patch-clamp recording from AFD to show that loss of GCY-8, but not of GCY-18 or GCY-23, reduces or eliminates ThRCs, identifying this rGC as a crucial signaling element. To learn more about thermotransduction and adaptation, we used behavioral screens and analysis of gene expression patterns to identify phosphodiesterases (PDEs) likely to contribute to thermotransduction. Deleting PDE-2 decouples the threshold for ThRC activation from ambient temperature, altering adaptation. We provide evidence that the conserved neuronal calcium sensor 1 protein also regulates the threshold for ThRC activation and propose a signaling network to account for ThRC activation and adaptation. Because PDEs play essential roles in diverse biological processes, including vertebrate phototransduction and olfaction, and regulation of smooth muscle contractility and cardiovascular function, this study has broad implications for understanding how extraordinary sensitivity and dynamic range is achieved in cyclic nucleotide–based signaling networks.

Understanding the physiological roles of the neuronal calcium sensor proteins

Calcium signalling plays a crucial role in the control of neuronal function and plasticity. Changes in neuronal Ca²⁺ concentration are detected by Ca²⁺-binding proteins that can interact with and regulate target proteins to modify their function. Members of the neuronal calcium sensor (NCS) protein family have multiple non-redundant roles in the nervous system. Here we review recent advances in the understanding of the physiological roles of the NCS proteins and the molecular basis for their specificity.