Severe deficiency of voltage-gated sodium channel NaV1.2 elevates neuronal excitability in adult mice

AbstractScn2a encodes voltage-gated sodium channel NaV1.2, which mediates neuronal firing. The current paradigm suggests that NaV1.2 gain-of-function variants enhance neuronal excitability resulting in epilepsy, whereas NaV1.2 deficiency impairs neuronal excitability contributing to autism. In this paradigm, however, why about a third of patients with NaV1.2 deficiency still develop seizures remains a mystery. Here we challenge the conventional wisdom, reporting that neuronal excitability is increased with severe NaV1.2 deficiency. Using a unique gene-trap knockout mouse model of Scn2a, we found enhanced intrinsic excitabilities of principal neurons in the cortico-striatal circuit, known to be involved in Scn2a-related seizures. This increased excitability is autonomous, and is reversible by genetic restoration of Scn2a expression in adult mice. Mechanistic investigation reveals a compensatory downregulation of potassium channels including KV1.1, which could be targeted to alleviate neuronal hyperexcitability. Our unexpected findings may explain NaV1.2 deficiency-related epileptic seizures in humans and provide molecular targets for potential interventions.TEASERSevere NaV1.2 deficiency results in neuronal hyperexcitability via the compensatory downregulation of potassium channels.HIGHLIGHTSSevere NaV1.2 deficiency results in enhanced excitability of medium spiny neurons (MSNs) and pyramidal neurons in adult mice;Increased neuronal excitability in MSNs is accompanied by elevated voltage threshold;NaV1.2 deficiency-related hyperexcitability is reversible with the restoration of Scn2a expression, and is autonomous;The expression of the KV1.1 channel has a compensatory reduction in neurons with NaV1.2 deficiency, and KV channels openers normalize the neuronal excitability;The enhanced excitability in brain slices translates to elevated in vivo firing commonly associated with seizures.

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Severe deficiency of the voltage-gated sodium channel NaV1.2 elevates neuronal excitability in adult mice

Cell Reports ◽

10.1016/j.celrep.2021.109495 ◽

2021 ◽

Vol 36 (5) ◽

pp. 109495

Author(s):

Jingliang Zhang ◽

Xiaoling Chen ◽

Muriel Eaton ◽

Jiaxiang Wu ◽

Zhixiong Ma ◽

...

Keyword(s):

Sodium Channel ◽

Neuronal Excitability ◽

Voltage Gated Sodium Channel ◽

Voltage Gated ◽

Adult Mice ◽

Severe Deficiency

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P38 Clinical pearl: pharmaceutical management of primary erythromelalgia (pe) (scn9a)

Archives of Disease in Childhood ◽

10.1136/archdischild-2017-314585.47 ◽

2018 ◽

Vol 103 (2) ◽

pp. e2.42-e2

Author(s):

William Batten

Keyword(s):

Pain Relief ◽

Sodium Channel ◽

Genetic Mutation ◽

Lower Limbs ◽

Therapeutic Drug ◽

List Type ◽

Voltage Gated Sodium Channel ◽

Voltage Gated ◽

Primary Erythromelalgia ◽

At Home

SituationPatient RL is a 7 year old female with a confirmed genetic diagnosis for Primary Erythromelalgia PE, with a heterozygous sequence change in the SCN9A gene: c.2623C>G, p.(Gln875Glu). This genetic mutation of SCN9A results in sodium chanellopathy specifically for the voltage gated sodium channel Nav1.7. This genetic mutation makes the Nav1.7 channel hypersensitive to stimulus and over activation.1 As a result, she suffers from severe intermittent episodes of bilateral erythema and burning pain of the lower limbs. These symptoms are difficult to manage and PE is also known as ‘man-on-fire syndrome’.1BackgroundPE in a child is a complex diagnosis with severely limited pharmacological treatments available. Inadequate pain relief was achieved with routine analgesics such as paracetamol and ibuprofen. A multidisciplinary team (MDT) approach including pharmacy was implemented with; review of available literature, alternative medications for relief of pain and other PE symptoms, advice on formulation and dosing.OutcomeWhen initially diagnosed, RL was frequently admitted to hospital for uncontrollable and pain and the family were unable to manage at home. Since her diagnosis and full MDT involvement, her pain relief has improved, her hospital admissions have decreased and her family are coping better at home. However, despite pharmacological interventions she is still not entirely free from pain and her other symptoms. Patient RL has also received intensive psychology input for coping strategies in managing her pain, and her parents have received psychological and social input to help them. She is managing to walk more and but still relies on her pushchair. Her current medication regimen is as follows: gabapentin, cetirizine, chlorphenamine, naproxen, paracetamol, clonidine, mexiletine, amitriptyline and topical application of amitriptyline and ketamine. Unsuccessful treatments included: magnesium supplementation, menthol in aqueous cream, lidocaine patches, tramadol and aspirin.Lessons learntThere is little information in the literature on the treatment of paediatric patients with PE and they are mainly case reports. Management of RL has been multidisciplinary with pharmacy playing an important role advising on treatment of anecdotal evidence, dosing and formulation advice, counselling, sourcing amitriptyline and ketamine gel and therapeutic drug monitoring for mexiletine. Future treatments we hope to trial include novel drugs still in development that specifically target the voltage gated sodium channel Nav1.7 such as raxatrigine.ReferenceLawrence J. Nav1.7: A new channel for pain treatment. The Pharmaceutical Journal2016;296:7887. Available from: http://www.pharmaceutical-journal.com/publications/the-pharmaceutical-journal/20200841.article [Accessed: 26 July 2016.

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Alternative splicing potentiates dysfunction of early-onset epileptic encephalopathy SCN2A variants

The Journal of General Physiology ◽

10.1085/jgp.201912442 ◽

2020 ◽

Vol 152 (3) ◽

Cited By ~ 6

Author(s):

Christopher H. Thompson ◽

Roy Ben-Shalom ◽

Kevin J. Bender ◽

Alfred L. George

Keyword(s):

Alternative Splicing ◽

Sodium Channel ◽

Early Onset ◽

Neuronal Excitability ◽

Epileptic Encephalopathy ◽

Developmentally Regulated ◽

Voltage Gated Sodium Channel ◽

Splice Isoforms ◽

Voltage Gated ◽

Splice Isoform

Epileptic encephalopathies are severe forms of infantile-onset epilepsy often complicated by severe neurodevelopmental impairments. Some forms of early-onset epileptic encephalopathy (EOEE) have been associated with variants in SCN2A, which encodes the brain voltage-gated sodium channel NaV1.2. Many voltage-gated sodium channel genes, including SCN2A, undergo developmentally regulated mRNA splicing. The early onset of these disorders suggests that developmentally regulated alternative splicing of NaV1.2 may be an important consideration when elucidating the pathophysiological consequences of epilepsy-associated variants. We hypothesized that EOEE-associated NaV1.2 variants would exhibit greater dysfunction in a splice isoform that is prominently expressed during early development. We engineered five EOEE-associated NaV1.2 variants (T236S, E999K, S1336Y, T1623N, and R1882Q) into the adult and neonatal splice isoforms of NaV1.2 and performed whole-cell voltage clamp to elucidate their functional properties. All variants exhibited functional defects that could enhance neuronal excitability. Three of the five variants (T236S, E999K, and S1336Y) exhibited greater dysfunction in the neonatal isoform compared with those observed in the adult isoform. Computational modeling of a developing cortical pyramidal neuron indicated that T236S, E999K, S1336Y, and R1882Q showed hyperexcitability preferentially in immature neurons. These results suggest that both splice isoform and neuronal developmental stage influence how EOEE-associated NaV1.2 variants affect neuronal excitability.

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CaMKII enhances voltage-gated sodium channel Nav1.6 activity and neuronal excitability

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.014062 ◽

2020 ◽

Vol 295 (33) ◽

pp. 11845-11865

Author(s):

Agnes S. Zybura ◽

Anthony J. Baucum ◽

Anthony M. Rush ◽

Theodore R. Cummins ◽

Andy Hudmon

Keyword(s):

Protein Kinase ◽

Sodium Channel ◽

Neuronal Excitability ◽

Cell Model ◽

Site Directed Mutagenesis ◽

Hek293 Cells ◽

Intracellular Loop ◽

Persistent Currents ◽

Voltage Gated Sodium Channel ◽

Voltage Gated

Nav1.6 is the primary voltage-gated sodium channel isoform expressed in mature axon initial segments and nodes, making it critical for initiation and propagation of neuronal impulses. Thus, Nav1.6 modulation and dysfunction may have profound effects on input-output properties of neurons in normal and pathological conditions. Phosphorylation is a powerful and reversible mechanism regulating ion channel function. Because Nav1.6 and the multifunctional Ca2+/CaM-dependent protein kinase II (CaMKII) are independently linked to excitability disorders, we sought to investigate modulation of Nav1.6 function by CaMKII signaling. We show that inhibition of CaMKII, a Ser/Thr protein kinase associated with excitability, synaptic plasticity, and excitability disorders, with the CaMKII-specific peptide inhibitor CN21 reduces transient and persistent currents in Nav1.6-expressing Purkinje neurons by 87%. Using whole-cell voltage clamp of Nav1.6, we show that CaMKII inhibition in ND7/23 and HEK293 cells significantly reduces transient and persistent currents by 72% and produces a 5.8-mV depolarizing shift in the voltage dependence of activation. Immobilized peptide arrays and nanoflow LC-electrospray ionization/MS of Nav1.6 reveal potential sites of CaMKII phosphorylation, specifically Ser-561 and Ser-641/Thr-642 within the first intracellular loop of the channel. Using site-directed mutagenesis to test multiple potential sites of phosphorylation, we show that Ala substitutions of Ser-561 and Ser-641/Thr-642 recapitulate the depolarizing shift in activation and reduction in current density. Computational simulations to model effects of CaMKII inhibition on Nav1.6 function demonstrate dramatic reductions in spontaneous and evoked action potentials in a Purkinje cell model, suggesting that CaMKII modulation of Nav1.6 may be a powerful mechanism to regulate neuronal excitability.

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