To investigate whether filtration of sporadic amyotrophic lateral sclerosis (sALS) cerebrospinal fluid (CSF) removes neurotoxic factors that cause motor neuron death.

ALS is a progressive neurodegenerative disease characterized by motor neuron death. Its sporadic form is the most prevalent, afflicting 90% of those with ALS. We previously showed that intrathecal delivery of sALS CSF into the cervical subarachnoid space of mice can induce motor disability and hallmark disease pathology including motor neuron loss and TDP-43 translocation. Removal of sALS CSF components larger than 5 kDa via filtration attenuated the neurotoxic capacity of sALS CSF in vivo. Here, we investigate whether 5 kDa filtration also removes neurotoxic factors in sALS CSF which induce human motor neuron death in vitro.   

sALS CSF was passed through a tangential flow 5 kDa hollow-fiber filter for 3 cycles to eliminate all components larger than 5 kDa. Human iPSC-derived motor neurons were cultured for 8 days and treated with either media, 50% sALS CSF in media, or 50% filtered sALS CSF in media. 24 hours after treatment, cells were fixed for ChAT and activated caspase-3 immunostaining. Area of motor neuron clusters was quantified as a measure of motor neuron survival.

sALS CSF induces death of human motor neurons, as indicated by significantly smaller ChAT⁺ clusters than motor neurons grown in media. However, human motor neurons treated with 5 kDa filtered sALS CSF had significantly larger cluster areas than sALS CSF-treated neurons, indicating that neurotoxic factors may be filtered out to attenuate sALS CSF-induced motor neuron death.

The neurotoxic factors in sALS CSF responsible for inducing human motor neuron death in vitro are larger than 5 kDa in size. Filtration through 5kDa filters removes these neurotoxic factors and successfully mitigates the neurotoxic capacity of sALS CSF.