Characterisation of TDP-43 expression in the Thy1-hTDP-43 ALS mouse model

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that results from the loss of upper and lower motor neurons. Despite a heterogeneous, complex genetic background, one aspect that connects 97% of ALS patients is the presence of abnormal protein aggregates in motor neurons with TDP-43 as the main constituent. Moreover, mutations in the TARDBP gene are also known to be causative in 4% of familial cases and 1% of sporadic ALS patients. This indicates that TDP-43 is central to ALS pathogenesis.

To investigate this key aspect of ALS, we used the Thy1-hTDP-43 mouse model, a severe model of ALS with a lifespan of 20-25 postnatal days (P). Here, we have quantified TDP-43 protein expression over the mouse lifespan, facilitating comparison with other disease phenotypes; such as motor neuron cell death and NMJ denervation. Using human-specific versus pan-mammalian antibodies for TDP-43, we compared the expression of pathological hTDP-43 and endogenous mouse TDP-43 in the spinal cord and brain, via western blotting. To document cell death, blinded motor neuron counts were performed at pre-symptomatic (P8), early-symptomatic (P15) and symptomatic (P17) timepoints, as well as at disease end-stage (P19-21).

Our results demonstrate a significant overexpression of pathological hTDP-43 pre-symptomatically, leading to an 8-fold increase in TDP-43 expression at end-stage in homozygous Tg/Tg mice. Interestingly, non-symptomatic heterozygous littermates also showed overexpression of hTDP-43 up to P15, where expression then plateaued at a two-fold increase compared to wild-types for up to 9 months. Motor neuron counts showed that there was a significant overall loss of motor neurons from the ventral horn in hTDP-43 Tg/Tg mice at end-stage (n=3 mice per genotype, N=18 spinal cord slices analysed per genotype, P-value=0.02). This detailed analysis of the time course of TDP-43 overexpression and motor neuron loss will allow us to investigate the order of pathological events in the Thy1-hTDP-43 model, including the timing of neuromuscular junction denervation compared to motor neuron cell death.