Amyotrophic lateral sclerosis-associated mutant VAPBP56S perturbs calcium homeostasis to disrupt axonal transport of mitochondria

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Abstract

A proline-to-serine substitution at position 56 in the gene encoding vesicle-associated membrane protein-associated protein B (VAPB; VAPBP56S) causes some dominantly inherited familial forms of motor neuron disease, including amyotrophic lateral sclerosis (ALS) type-8. Here, we show that expression of ALS mutant VAPBP56S but not wild-type VAPB in neurons selectively disrupts anterograde axonal transport of mitochondria. VAPBP56S-induced disruption of mitochondrial transport involved reductions in the frequency, velocity and persistence of anterograde mitochondrial movement. Anterograde axonal transport of mitochondria is mediated by the microtubule-based molecular motor kinesin-1. Attachment of kinesin-1 to mitochondria involves the outer mitochondrial membrane protein mitochondrial Rho GTPase-1 (Miro1) which acts as a sensor for cytosolic calcium levels ([Ca(2+)]c); elevated [Ca(2+)]c disrupts mitochondrial transport via an effect on Miro1. To gain insight into the mechanisms underlying the VAPBP56S effect on mitochondrial transport, we monitored [Ca(2+)]c levels in VAPBP56S-expressing neurons. Expression of VAPBP56S but not VAPB increased resting [Ca(2+)]c and this was associated with a reduction in the amounts of tubulin but not kinesin-1 that were associated with Miro1. Moreover, expression of a Ca(2+) insensitive mutant of Miro1 rescued defective mitochondrial axonal transport and restored the amounts of tubulin associated with the Miro1/kinesin-1 complex to normal in VAPBP56S-expressing cells. Our results suggest that ALS mutant VAPBP56S perturbs anterograde mitochondrial axonal transport by disrupting Ca(2+) homeostasis and effecting the Miro1/kinesin-1 interaction with tubulin.

Original languageEnglish
Pages (from-to)1979-88
Number of pages10
JournalHuman Molecular Genetics
Volume21
Issue number9
DOIs
Publication statusPublished - 1 May 2012

Keywords

  • Amino Acid Substitution
  • Amyotrophic Lateral Sclerosis/genetics
  • Animals
  • Axonal Transport/genetics
  • Base Sequence
  • Calcium/metabolism
  • HEK293 Cells
  • Homeostasis
  • Humans
  • Kinesins/metabolism
  • Mitochondria/metabolism
  • Mitochondrial Proteins/genetics
  • Movement
  • Mutagenesis, Site-Directed
  • Mutant Proteins/genetics
  • Neurons/metabolism
  • Plasmids/genetics
  • Rats
  • Recombinant Proteins/genetics
  • Time-Lapse Imaging
  • Transfection
  • Tubulin/metabolism
  • Vesicular Transport Proteins/genetics
  • rho GTP-Binding Proteins/genetics

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