title: Amyotrophic lateral sclerosis-associated mutant VAPBP56S perturbs calcium homeostasis to disrupt axonal transport of mitochondria.
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.
authors.affiliation: Department of Neuroscience, Institute of Psychiatry, Kings College London, London, UK.
authors.forename: Gábor M
authors.initials: GM
authors.lastname: Mórotz
authors.forename: Kurt J
authors.initials: KJ
authors.lastname: De Vos
authors.forename: Alessio
authors.initials: A
authors.lastname: Vagnoni
authors.forename: Steven
authors.initials: S
authors.lastname: Ackerley
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Shaw
authors.forename: Christopher C J
authors.initials: CC
authors.lastname: Miller
mesh_terms: D019943:Amino Acid Substitution; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001370:Axonal Transport / Q000235:genetics* / Q000502:physiology*; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D057809:HEK293 Cells; D006706:Homeostasis; D006801:Humans; D016547:Kinesins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D009068:Movement; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics* / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D059008:Time-Lapse Imaging; D014162:Transfection; D014404:Tubulin / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C488101:KIF5B protein, human; D024101:Mitochondrial Proteins; D050505:Mutant Proteins; D011994:Recombinant Proteins; D014404:Tubulin; C496748:VAPB protein, human; D033921:Vesicular Transport Proteins; C473124:RHOT1 protein, human; D016547:Kinesins; D020741:rho GTP-Binding Proteins; D002118:Calcium