Functional study of NIPA2 mutations identified from the patients with childhood absence epilepsy

PLoS One. 2014 Oct 27;9(10):e109749. doi: 10.1371/journal.pone.0109749. eCollection 2014.

Abstract

Recently many genetic mutations that are associated with epilepsy have been identified. The protein NIPA2 (non-imprinted in Prader-Willi/Angelman syndrome region protein 2) is a highly selective magnesium transporter encoded by the gene NIPA2 in which we have found three mutations (p.I178F, p.N244S and p.N334_E335insD) within a population of patients with childhood absence epilepsy (CAE). In this study, immunofluorescence labeling, inductively coupled plasma-optical emission spectroscopy (ICP-OES), MTT metabolic rate detection and computational modeling were utilized to elucidate how these mutations result in CAE. We found in cultured neurons that NIPA2 (wild-type) proteins were localized to the cell periphery, whereas mutant proteins were not effectively trafficked to the cell membrane. Furthermore, we found a decrease in intracellular magnesium concentration in the neurons transfected with mutant NIPA2, but no effect on the survival of neurons. To understand how low intracellular magnesium resulted in hyperexcitability, we built and analyzed a computational model to simulate the effects of mutations. The model suggested that lower intracellular magnesium concentration enhanced synaptic N-methyl-D-aspartate receptor (NMDAR) currents. This study primarily reveals that a selective magnesium transporter NIPA2 may play a role in the pathogenesis of CAE.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cation Transport Proteins
  • Cell Survival / genetics
  • Child
  • Child, Preschool
  • Cytoplasm / metabolism
  • Epilepsy, Absence / genetics*
  • Epilepsy, Absence / metabolism
  • Gene Expression
  • Genetic Association Studies
  • Humans
  • Magnesium / metabolism
  • Membrane Proteins / genetics*
  • Membrane Proteins / metabolism
  • Mutation*
  • Neurons / metabolism
  • Protein Transport
  • Receptors, N-Methyl-D-Aspartate / metabolism
  • Transfection

Substances

  • Cation Transport Proteins
  • Membrane Proteins
  • NIPA2 protein, human
  • Receptors, N-Methyl-D-Aspartate
  • Magnesium

Grants and funding

This work was supported by National Natural Science Fund of China (Grant Number 81271439 to Y.J.); National Key Research Project “973”, sub-project (Grant No. 2012CB944602 to Y.J.); National Science Funding (Grant Number 1135581 to T.N.); Epilepsy Foundation (Grant Number 190960 to T.N.); China Scholarship Council Program (Student Number 201206010800 to H.X.); Academic Scholarship for Doctoral Candidates (Ministry of Education, P.R. China to H.X.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.