Characterization of the Properties of a Novel Mutation in VAPB in Familial Amyotrophic Lateral Sclerosis

Abstract

Following the mutation screening of genes known to cause amyotrophic lateral sclerosis (ALS) in index cases from 107 familial ALS (FALS) kindred, a point mutation was identified in vesicle-associated membrane protein-associated protein B (VAPB), or VAMP-associated protein B, causing an amino acid change from threonine to isoleucine at codon 46 (T46I) in one FALS case but not in 257 controls. This is an important finding because it is only the second mutation identified in this gene that causes ALS. In order to investigate the pathogenic effects of this mutation, we have used a motor neuron cell line and tissue-specific expression of the mutant protein in Drosophila. We provide substantial evidence for the pathogenic effects of this mutation in abolishing the effect of wild type VAPB in the unfolded protein response, promoting ubiquitin aggregate formation, and activating neuronal cell death. We also report that expression of the mutant protein in the Drosophila motor system induces aggregate deposition, endoplasmic reticulum disorganization, and chaperone up-regulation both in neurons and in muscles. Our integrated analysis of the pathogenic effect of the T46I mutation and the previously identified P56S mutation indicate extensive commonalities in the disease mechanism for these two mutations. In summary, we show that this newly identified mutation in human FALS has a pathogenic effect, supporting and reinforcing the role of VAPB as a causative gene of ALS.

Amyotrophic Lateral Sclerosis Mutant VAPB Causes a Nuclear Envelope Defect

“…Familial ALS8 is caused by a P56S mutation in the vesicleassociated membrane protein-associated protein B and C (VAPB) gene (Nishimura et al, 2004;Chen et al, 2010). Overexpression of the VAPB P56S mutant protein leads to formation of large endoplasmic reticulum (ER)-derived membranes (Nishimura et al, 2004;Kanekura et al, 2006;Teuling et al, 2007;Prosser et al, 2008;Suzuki et al, 2009).…”

Sequestosome-1 (SQSTM1) sequence variants in ALS cases in the UK: prevalence and coexistence of SQSTM1 mutations in ALS kindred with PDB

“…This is a subset of a larger cohort in which known mutations have been previously characterised and has the following distribution of FALS mutations, C9ORF72 (30.2%), SOD1 (18.0%), TARDBP (4.3%), FUS (2.2%), DAO (0.72%) and VAPB (0.72%). [14][15][16][17][18][19] This study employed ALS cases, presenting with motor neuron symptoms and diagnosed as ALS according to EL-Escorial criteria, from the United Kingdom (Imperial College Healthcare NHS trust). All ALS patients were positive for a familial history (FALS), and each patient was an index case from a separate kindred.…”

Genetics of Amyotrophic Lateral Sclerosis

“…A different mutation (T46I) was detected in a family from the UK (Chen et al, 2010). The VAPB protein has been implicated in various cellular processes including the formation of the presynaptic terminal in neurons, vesicle trafficking and the unfolded protein response (Chen et al, 2010). Transgenic mice overexpressing ALS mutant VAPB or wild-type VAPB do not develop an overt motor neuron phenotype.…”

“…The same mutation was also identified in six additional families with different clinical courses including, ALS8, late-onset spinal muscular atrophy and typical severe ALS with rapid progression. A different mutation (T46I) was detected in a family from the UK (Chen et al, 2010). The VAPB protein has been implicated in various cellular processes including the formation of the presynaptic terminal in neurons, vesicle trafficking and the unfolded protein response (Chen et al, 2010).…”