Sporadic ALS cerebrospinal fluid induces pathological translocation of TDP-43 in motor neurons

Objective: To assess whether cytoplasmic translocation of Transactive response DNA Binding Protein 43 (TDP-43) is induced in motor neurons following intrathecal injection of amyotrophic lateral sclerosis (ALS) cerebrospinal fluid (CSF) in mice.

Background: ALS is a progressive neurodegenerative disorder characterized by motor neuron death. Only 5-10% of ALS cases are familial (fALS) while the majority occur sporadically (sALS). One hallmark of ALS is TDP-43 aggregation in the cytoplasm. We previously reported that intrathecal delivery of sALS, but not fALS CSF, induces motor deficits and motor neuron degeneration in mice. Here, we investigated whether differences in CSF neurotoxicity are associated with induction of pathological TDP-43 expression.

Design/Methods: CSF obtained from sALS and fALS patients was delivered intrathecally to 8-10-week-old female C57BL/6 mice. Mice were injected with 3uL of sALS, SOD1, C9orf72, TARDBP CSF or 5kDa filtered sALS CSF. 5kDa filtered sALS CSF was obtained by passing sALS CSF through a 5kDa hollow-fiber filter. Control mice received either saline, CSF from healthy individuals or multiple sclerosis patients. Forelimb deficits were assessed at 1-day post injection (DPI), then mice were perfused for histological analysis. TDP-43 localization was assessed by co-staining tissue with anti-TDP-43 and anti-ChAT antibodies.

Results: The percentage of ChAT+ motor neurons expressing cytoplasmic TDP-43 was significantly higher in sALS CSF-injected mice compared to saline and SOD1 CSF injected mice. Cytoplasmic TDP-43 expression was higher in C9 and TARDBP CSF-injected mice, but differences were not statistically significant compared to SOD1 CSF or control groups. Cytoplasmic expression of TDP-43 was significantly reduced in filtered sALS CSF-injected mice.

Conclusions: TDP-43 mislocalization was specific to sALS CSF-injected mice, which further validates our animal model of sALS and reveals distinct disease mechanisms underlying sALS and fALS. Reduced induction of pathological TDP-43 expression by filtered sALS CSF supports potential therapeutic value of CSF pheresis in sALS.