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Severe deficiency of the voltage-gated sodium channel Na_V1.2 elevates neuronal excitability in adult mice.

ABSTRACT: Scn2a encodes the voltage-gated sodium channel Na_V1.2, a main mediator of neuronal action potential firing. The current paradigm suggests that Na_V1.2 gain-of-function variants enhance neuronal excitability, resulting in epilepsy, whereas Na_V1.2 deficiency impairs neuronal excitability, contributing to autism. However, this paradigm does not explain why ∼20%-30% of individuals with Na_V1.2 deficiency still develop seizures. Here, we report the counterintuitive finding that severe Na_V1.2 deficiency results in increased neuronal excitability. Using a Na_V1.2-deficient mouse model, we show enhanced intrinsic excitability of principal neurons in the prefrontal cortex and striatum, brain regions known to be involved in Scn2a-related seizures. This increased excitability is autonomous and reversible by genetic restoration of Scn2a expression in adult mice. RNA sequencing reveals downregulation of multiple potassium channels, including K_V1.1. Correspondingly, K_V channel openers alleviate the hyperexcitability of Na_V1.2-deficient neurons. This unexpected neuronal hyperexcitability may serve as a cellular basis underlying Na_V1.2 deficiency-related seizures.

SUBMITTER: Zhang J

PROVIDER: S-EPMC8382316 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:See Lerche (doi:10.1093/brain/awy073) for a scientific commentary on this article.Proline-rich transmembrane protein 2 (PRRT2) is the causative gene for a heterogeneous group of familial paroxysmal neurological disorders that include seizures with onset in the first year of life (benign familial infantile seizures), paroxysmal kinesigenic dyskinesia or a combination of both. Most of the PRRT2 mutations are loss-of-function leading to haploinsufficiency and 80% of the patients carry the same frameshift mutation (c.649dupC; p.Arg217Profs*8), which leads to a premature stop codon. To model the disease and dissect the physiological role of PRRT2, we studied the phenotype of neurons differentiated from induced pluripotent stem cells from previously described heterozygous and homozygous siblings carrying the c.649dupC mutation. Single-cell patch-clamp experiments on induced pluripotent stem cell-derived neurons from homozygous patients showed increased Na+ currents that were fully rescued by expression of wild-type PRRT2. Closely similar electrophysiological features were observed in primary neurons obtained from the recently characterized PRRT2 knockout mouse. This phenotype was associated with an increased length of the axon initial segment and with markedly augmented spontaneous and evoked firing and bursting activities evaluated, at the network level, by multi-electrode array electrophysiology. Using HEK-293 cells stably expressing Nav channel subtypes, we demonstrated that the expression of PRRT2 decreases the membrane exposure and Na+ current of Nav1.2/Nav1.6, but not Nav1.1, channels. Moreover, PRRT2 directly interacted with Nav1.2/Nav1.6 channels and induced a negative shift in the voltage-dependence of inactivation and a slow-down in the recovery from inactivation. In addition, by co-immunoprecipitation assays, we showed that the PRRT2-Nav interaction also occurs in brain tissue. The study demonstrates that the lack of PRRT2 leads to a hyperactivity of voltage-dependent Na+ channels in homozygous PRRT2 knockout human and mouse neurons and that, in addition to the reported synaptic functions, PRRT2 is an important negative modulator of Nav1.2 and Nav1.6 channels. Given the predominant paroxysmal character of PRRT2-linked diseases, the disturbance in cellular excitability by lack of negative modulation of Na+ channels appears as the key pathogenetic mechanism.

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Severe deficiency of the voltage-gated sodium channel Na_V1.2 elevates neuronal excitability in adult mice.

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

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OmicsDI is part of the ELIXIR infrastructure

Tweets

Severe deficiency of the voltage-gated sodium channel Na_V1.2 elevates neuronal excitability in adult mice.