Exp Neurobiol.  2018 Dec;27(6):550-563. 10.5607/en.2018.27.6.550.

A De Novo RAPGEF2 Variant Identified in a Sporadic Amyotrophic Lateral Sclerosis Patient Impairs Microtubule Stability and Axonal Mitochondria Distribution

Affiliations
  • 1Department of Brain and Cognitive Sciences and Dental Research Institute, Seoul National University, Seoul 08826, Korea. seunglee@snu.ac.kr
  • 2Department of Neurology, College of Medicine, Hanyang University, Seoul 04763, Korea. kimsh1@hanyang.ac.kr
  • 3Department of Laboratory Medicine, College of Medicine, Hanyang University, Seoul 04763, Korea.
  • 4Department of Molecular Neuroscience, College of Medicine, Dong-A University, Busan 49201, Korea.
  • 5Green Cross Genome Corporation, Yongin 16924, Korea. changski.md@gmail.com

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that is frequently linked to microtubule abnormalities and mitochondrial trafficking defects. Whole exome sequencing (WES) of patient-parent trios has proven to be an efficient strategy for identifying rare de novo genetic variants responsible for sporadic ALS (sALS). Using a trio-WES approach, we identified a de novo RAPGEF2 variant (c.4069G>A, p.E1357K) in a patient with early-onset sALS. To assess the pathogenic effects of this variant, we have used patient-derived skin fibroblasts and motor neuron-specific overexpression of the RAPGEF2-E1357K mutant protein in Drosophila. Patient fibroblasts display reduced microtubule stability and defective microtubule network morphology. The intracellular distribution, ultrastructure, and function of mitochondria are also impaired in patient cells. Overexpression of the RAPGEF2 mutant in Drosophila motor neurons reduces the stability of axonal microtubules and disrupts the distribution of mitochondria to distal axons and neuromuscular junction (NMJ) synapses. We also show that the recruitment of the pro-apoptotic protein BCL2-associated X (BAX) to mitochondria is significantly increased in patient fibroblasts compared with control cells. Finally, increasing microtubule stability through pharmacological inhibition of histone deacetylase 6 (HDAC6) rescues defects in the intracellular distribution of mitochondria and BAX. Overall, our data suggest that the RAPGEF2 variant identified in this study can drive ALS-related pathogenic effects through microtubule dysregulation.

Keyword

Amyotrophic lateral sclerosis; Whole exome sequencing; RAPGEF2; Missense mutation; Microtubules; Mitochondria

MeSH Terms

Amyotrophic Lateral Sclerosis*
Axons*
Drosophila
Exome
Fibroblasts
Histone Deacetylases
Humans
Microtubules*
Mitochondria*
Motor Neurons
Mutant Proteins
Mutation, Missense
Neurodegenerative Diseases
Neuromuscular Junction
Skin
Synapses
Histone Deacetylases
Mutant Proteins
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