Synaptic changes contribute to persistent extra-motor behaviour deficits in amyotrophic lateral sclerosis

Extra-motor symptoms are increasingly recognised in amyotrophic lateral sclerosis (ALS), encompassing cognitive, social, and behavioural deficits. TAR DNA binding protein 43 (TDP-43) pathology is the central disease marker of almost all cases of ALS and approximately half of frontotemporal dementia (FTD). However, the mechanisms linking TDP-43 pathology with extra-motor symptoms in TDP-43-associated neurodegenerative diseases remain unresolved. In this study, we used the rNLS8 mouse model, which expresses human TDP-43 with an ablated nuclear localisation sequence (hTDP-43∆NLS) in a doxycycline-regulatable manner causing progressive motor decline reminiscent of ALS, to delineate molecular changes associated with disease-relevant phenotypes. We found that in addition to previously reported dramatic motor decline, rNLS8 mice also develop extra-motor phenotypes consistent with FTD, including disinhibition-like and anxiety-like behaviours, and social interaction impairments. These changes began in the earliest disease stages and remained readily detectable even when rNLS8 mice became severely motor impaired. Notably, extra-motor deficits persisted in rNLS8 mice that had recovered motor function upon hTDP-43∆NLS transgene suppression. This correlates with widespread mis-splicing of RNA in rNLS8 cortex at disease onset with n = 814 genes showing differential exon usage, a molecular phenotype of TDP-43 loss of function. Mis-splicing persists in the rNLS8 cortex in recovery and may represent lasting impacts of cytoplasmic TDP-43 expression. Further, proteomics analysis of the cortex of rNLS8 mice revealed depletion of synaptic proteins, particularly those involved in glutamatergic signalling pathways, which also persisted following hTDP-43∆NLS transgene suppression. Similar changes to the glutamatergic pathway were detected in transcriptomic and proteomic datasets from human ALS and FTD post-mortem cortex. Our findings suggest that targeting glutamatergic synaptic components may be an avenue to correct extra-motor deficits associated with TDP-43 pathology.