Abnormal increased mTOR signaling regulates seizure threshold in Dravet syndrome

Excessive activation of mTOR has been observed in the brains of mouse models for Dravet syndrome. We aim to confirm whether that the overactivation of mTOR contributes to the neuropathological changes leading to epileptogenesis and neurobehavior deficits to support a novel pharmacological therapeutic approach for Dravet syndrome. The mTOR inhibitor everolimus, as a clinical antiseizure medication, was utilized to investigate whether mTOR is involved in hyperthermia-induced seizures, anxiety-like, and autism-like behaviors, as well as to explore potential pathogenic mechanisms in Scn1a^E1099X/+ mice, a model of Dravet syndrome. First, we found that mTOR signaling was upregulated in hippocampus tissues and neural cultures derived from Scn1a^E1099X/+ mice prior to seizure onset. Behaviorally, everolimus increased the seizure threshold and improved anxiety-like and autism-like behaviors in Scn1a^E1099X/+ mice. Electrophysiologically, everolimus reduced the frequency of spontaneous excitatory postsynaptic currents in dentate granule neurons from Scn1a^E1099X/+ mice. Biochemically, everolimus prevented hyperthermia-induced phosphorylation of hippocampal S6 ribosome in hippocampus, and it delayed hyperthermia-induced increase of cytosolic Ca²⁺ level in primary neuronal cultures derived from Scn1a^E1099X/+ mice. Our results provide the evidence that overactivated mTOR as an important neuropathological change which regulates seizure threshold, impairments of neurobehavior, neuronal glutamatergic transmission and intracellular Ca²⁺ levels in Scn1a^E1099X/+ mice. Inhibition of mTOR is a potential pharmacological therapeutic approach.