MTOR-dependent alterations of Kv1.1 subunit expression in the neuronal subset-specific Pten knockout mouse model of cortical dysplasia with epilepsy

Lena H Nguyen,Anne E Anderson

doi:10.1038/s41598-018-21656-8

Abstract

Cortical dysplasia (CD) is a common cause for intractable epilepsy. Hyperactivation of the mechanistic target of rapamycin (mTOR) pathway has been implicated in CD; however, the mechanisms by which mTOR hyperactivation contribute to the epilepsy phenotype remain elusive. Here, we investigated whether constitutive mTOR hyperactivation in the hippocampus is associated with altered voltage-gated ion channel expression in the neuronal subset-specific Pten knockout (NS-Pten KO) mouse model of CD with epilepsy. We found that the protein levels of Kv1.1, but not Kv1.2, Kv1.4, or Kvβ2, potassium channel subunits were increased, along with altered Kv1.1 distribution, within the hippocampus of NS-Pten KO mice. The aberrant Kv1.1 protein levels were present in young adult (≥postnatal week 6) but not juvenile (≤postnatal week 4) NS-Pten KO mice. No changes in hippocampal Kv1.1 mRNA levels were found between NS-Pten KO and WT mice. Interestingly, mTOR inhibition with rapamycin treatment at early and late stages of the pathology normalized Kv1.1 protein levels in NS-Pten KO mice to WT levels. Together, these studies demonstrate altered Kv1.1 protein expression in association with mTOR hyperactivation in NS-Pten KO mice and suggest a role for mTOR signaling in the modulation of voltage-gated ion channel expression in this model.

Highlights

Cortical dysplasia (CD) and other malformations of cortical development (MCDs) are highly associated with severe and intractable epilepsy, a condition characterized by spontaneous, recurrent seizures, and account for the first and third most common cause for epilepsy surgery in children and adults, respectively[1,2,3]
Further evaluation using immunostaining for phosphatase and tensin homolog (Pten) revealed, in agreement with previous reports[21,22], marked loss of Pten staining in the dentate gyrus (DG) granule cell layer of NS-Pten KO compared to WT mice (Fig. 1C)
Given the emerging involvement for mechanistic target of rapamycin (mTOR) signaling in voltage-gated ion channel expression[14,34], one candidate mechanism by which mTOR dysregulation promotes epilepsy in CD is through remodeling of voltage-gated ion channel expression

Summary

Introduction

Cortical dysplasia (CD) and other malformations of cortical development (MCDs) are highly associated with severe and intractable epilepsy, a condition characterized by spontaneous, recurrent seizures, and account for the first and third most common cause for epilepsy surgery in children and adults, respectively[1,2,3]. MTORC2 consists of mTOR associated with rictor, Sin[1], and mLST8, and is a rapamycin-insensitive complex largely known for its role in regulating actin dynamics. Voltage-gated ion channels play critical roles in the regulation of neuronal excitability, and dysregulation of ion channel function, localization, and expression have been associated with hyperexcitability, increased seizure susceptibility, and epilepsy in humans and animal models[12,13]. Mice with neuronal-specific deletion of phosphatase and tensin homolog (Pten), a negative regulator of mTOR whose loss-of-function leads to mTOR hyperactivation, show decreased expression of Kv4.2 potassium channels[15]. MTOR dysregulation could potentially contribute to hyperexcitability and recurrent seizures by altering the protein expression of voltage-gated potassium channels. Kv1 channels regulate action potential duration, initiation, and propagation as well as membrane repolarization and neurotransmitter release, and dysfunction in Kv1 channels has been linked to epilepsy[12,13,18,19]

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