Downregulation of VAPB expression in motor neurons derived from induced pluripotent stem cells of ALS8 patients

Abstract

Amyotrophic lateral sclerosis (ALS) is an incurable neuromuscular disease that leads to a profound loss of life quality and premature death. Around 10% of the cases are inherited and ALS8 is an autosomal dominant form of familial ALS caused by mutations in the vamp-associated protein B/C (VAPB) gene. The VAPB protein is involved in many cellular processes and it likely contributes to the pathogenesis of other forms of ALS besides ALS8. A number of successful drug tests in ALS animal models could not be translated to humans underscoring the need for novel approaches. The induced pluripotent stem cells (iPSC) technology brings new hope, since it can be used to model and investigate diseases in vitro. Here we present an additional tool to study ALS based on ALS8-iPSC. Fibroblasts from ALS8 patients and their non-carrier siblings were successfully reprogrammed to a pluripotent state and differentiated into motor neurons. We show for the first time that VAPB protein levels are reduced in ALS8-derived motor neurons but, in contrast to over-expression systems, cytoplasmic aggregates could not be identified. Our results suggest that optimal levels of VAPB may play a central role in the pathogenesis of ALS8, in agreement with the observed reduction of VAPB in sporadic ALS.

Nucleocytoplasmic transport defect in a North American patient with ALS8

“…We did not detect any difference in the localization or amount of mutant VAPB compared to control, consistent with previous observations in patient cells 7. We used cells with a physiologically appropriate level of VAPB expression, in contrast to earlier studies with overexpression models which showed decreased levels of soluble mutant protein 9…”

“…In overexpression cell models the P56S mutant protein is mislocalized and coaggregated with the wild‐type VAPB 6. However, an ALS8 motor neuron cell model was found to have reduced levels of the P56S mutant protein without mislocalization 7. Some studies have shown that mutant VAPB results in endoplasmic reticulum (ER) stress, and unfolded protein response (UPR) activation, while other studies have shown a loss of IRE1a activated UPR with the P56S mutation 6, 8, 9.…”

New In Vitro Models to Study Amyotrophic Lateral Sclerosis

“…One other important limitation of this in vitro model is that cells differentiated from induced pluripotent stem cells often reflect only certain aspects of disease pathophysiology and it often takes several weeks before such abnormalities can be recorded and/or the observed characteristics are very mild (14,38). Observations from other neurological disorders, such as Alzheimer's (62) and Parkinson's disease (63), show a similar trend as what we have observed in ALS.…”

“…These cells also did not display any phenotype, despite reduced levels of VAPB. This finding was in contrast with what was shown in transgenic animal models carrying mutant VAPB, where cytoplasmic aggregates represented a hallmark of the disease (38). Although it is impossible to draw general conclusions with only one patient line, this discrepancy might highlight one of the main advantages of using patient-derived cells to model gene mutation-related ALS: the absence of artifacts deriving from transgene overexpression.…”

Modeling Williams syndrome with induced pluripotent stem cells

“…21 Such advancement has opened up new possibilities that could greatly benefit the medical research, including therapeutic applications and disease modeling. [22][23][24][25][26] First, unlike primary patient cells, which are limited in quantity, iPSCs provide infinite storable source for studies requiring large amount of cells such as highthroughput drug screening. Second, human iPSCderived cells are more physiologically relevant than animal models and available transformed cell lines.…”