Motor Neuron Disease-Associated Mutant Vesicle-Associated Membrane Protein-Associated Protein (VAP) B Recruits Wild-Type VAPs into Endoplasmic Reticulum-Derived Tubular Aggregates

Abstract

The vesicle-associated membrane protein-associated proteins (VAPs) VAPA and VAPB interact with lipid-binding proteins carrying a short motif containing two phenylalanines in an acidic tract (FFAT motif) and targets them to the cytosolic surface of the endoplasmic reticulum (ER). A genetic mutation (P56S) in the conserved major sperm protein homology domain of VAPB has been linked to motorneuron degeneration in affected amyotrophic lateral sclerosis (ALS) patients. We report that in the CNS, VAPB is abundant in motor neurons and that the P56S substitution causes aggregation of mutant VAPB in immobile tubular ER clusters, perturbs FFAT-motif binding, and traps endogenous VAP in mutant aggregates. Expression of mutant VAPB or reduction of VAP by short hairpin RNA in primary neurons causes Golgi dispersion and cell death. VAPA and VAPB are reduced in human ALS patients and superoxide dismutase 1 (SOD1)-ALS-transgenic mice, suggesting that VAP family proteins may be involved in the pathogenesis of sporadic and SOD1-linked ALS. Our data support a model in which reduced levels of VAP family proteins result in decreased ER anchoring of lipid-binding proteins and cause motor neuron degeneration.

Amyotrophic Lateral Sclerosis Mutant VAPB Causes a Nuclear Envelope Defect

“…1A-C). The vacuole-like structures probably correspond to the dilated membranes viewed under light microscopy in cells expressing mutant VAPB (Kanekura et al, 2006;Teuling et al, 2007;Prosser et al, 2008). Interestingly, ,75% of these cells also showed a prominent nuclear envelope defect characterized by separation of the INM and ONM at discrete regions (Fig.…”

“…Convoluted ER tubules have been observed in HeLa cells overexpressing mutant VAPB (Teuling et al, 2007;Fasana et al, 2010), and these were also evident in some cells. However, the most prominent features in cells overexpressing mutant VAPB alone or together with AAAT were large cytoplasmic vacuole-like structures and a dilated or 'herniated' nuclear envelope (Fig.…”

“…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). VAPB is an integral membrane protein with an N-terminal major sperm protein (MSP) domain and a C-terminal transmembrane domain.…”

A VAPB e a Esclerose Lateral Amiotrófica

“…Afterward, an ALS (47) model developed in our laboratory by Mitne-Neto et al (48), based on ALS8 patients' cells, has demonstrated that there is a reduction on the VAPB protein levels along motor neuron differentiation from iPSCs. These results complement other studies that show VAPB reduced levels in SALS patients and in SOD1 mice (49,50). These and other findings (51,52) strengthen the evidences that iPSC-derived motor neurons can recapitulate the disease phenotype.…”

Genetics of Amyotrophic Lateral Sclerosis

“…However, transgenic mice overexpressing ALS mutant but not wild-type VAPB show TAR DNA-binding protein 43 (TDP-43) positive cytoplasmic inclusions, a pathological hallmark of ALS (Tudor et al, 2010). It has been suggested that mutant VAPB exerts a dominant-negative effect by forming dimeric complexes with wild-type VAPB thereby recruiting it into aggregates (Teuling et al, 2007).…”