Subtype-specific downregulation of voltage-gated sodium channels shapes neuronal responses to neuroinflammation

Abstract

Epilepsy is one of the most common neurological disorders, affecting more than 50 million people worldwide. Among the genetic etiologies of epilepsy, variants in genes coding for ion channels are vastly represented and characterized. Notably, loss-of-function (LoF) mutations in voltage-gated sodium channels (NaV) genes can result in a wide range of phenotypes including West syndrome, autism spectrum disorder, or Dravet Syndrome. Although the implication of NaV subtypes in epileptic syndromes and the relationship between seizures and inflammation have been extensively described, subtype-specific neuronal responses to inflammation in the context of NaV loss-of-function remain poorly understood. In this study, we investigated the consequences of subtype-specific downregulation of NaV expression in primary mouse cortical neurons. Using shRNA-mediated silencing of Scn1a, Scn2a, or Scn8a, we generated neuronal cultures with reduced expression of NaV1.1, NaV1.2, or NaV1.6 and evaluated neuronal survival, inflammatory gene expression, and global transcriptomic responses under basal conditions and following an inflammatory challenge. Subtype-specific NaV downregulations did not produce a uniform phenotype. Rather, minor differences under basal conditions led to important discrepancies following exposure to an inflammatory stimulus. Notably, NaV1.1 reduction was associated with synaptic transcriptional changes, whereas NaV1.6 downregulation led to a substantial inflammatory signaling remodeling. Our observations suggest that the consequences of NaV dysfunction are not only determined by their role in neuronal excitability but also depend on subtype-specific responses to inflammatory cues. They notably shed light on the relevance of inflammatory events in the onset and progression of epileptic syndromes related to NaV loss-of-function mutations.