Characterisation of a model of ALS8 in the rat
Amyotrophic lateral sclerosis 8 (ALS8) is a late-onset slow-progressing form of motor neurone disease caused by a missense mutation replacing cytosine with thymine in the VAMP-associated protein B (vapB) gene, leading to a proline to serine replacement at position 56 (P56S) in the protein. The vapB protein is ubiquitously expressed in humans and located on the endoplasmic reticulum (ER). It is involved in intracellular signalling through two phenylalanine in a fatty acidic tract (FFAT)-like motifs on target proteins binding the major sperm protein domain (MSP) which can also cleave for extracellular signalling. The vapBP56S mutation interferes with MSP cleavage and vapB function by preventing cleavage of the MSP domain. CRISPR with long single stranded DNA inducing conditional knockout alleles (CLICK) was used to generate founders of a colony, with heterozygous (vapBP56S/+), homozygous (vapBP56S/P56S), and knockout (vapB-/-) offspring. A cohort was aged to 17-18 months in a longitudinal study with gait being assessed at 6, 12, and 18 months. Male vapBP56S/P56S, female vapBP56S/P56S and female vapB-/- exerted less pressure on their paws at 18 months. Tissue was collected at 18 months and analysed. There were fewer motor neurons (MN) in the lumbar spinal cord of vapBP56S/+ and vapBP56S/P56S, and MN were smaller in vapBP56S/P56S. TDP-43 pathology was present in vapB-/- motor neurons, and syntaxin 1A signal was reduced in lumbar spinal homogenates, but glial activation was absent. These results show that this rat model could help to provide insight into the initiation and propagation of ALS8.