ALS is a devastating neurodegenerative disease which results in motor neuron degeneration in the brain and spinal cord. Our previous research identified ApoB as a neurotoxic factor as it is upregulated in the cerebrospinal fluid (CSF) of ALS patients and can induce motor disability and motor neuron degeneration in vivo in mice, as well as death of human motor neurons in vitro. Here, we investigate whether astrocytes play a role in exacerbating or protecting against ApoB-induced motor neuron death.

Primary human astrocytes were plated on matrigel/DMEM-F12-coated chamber slides and grown in astrocyte growth media (AGM) overnight. The next day, the AGM was replaced with motor neuron maintenance media (MNMM) and iPSC-derived human motor neurons were plated directly on top of the astrocytes or on coated slides without astrocytes. On day 9, cells were either treated with 1 ng/µL ApoB diluted in MNMM or 50% ALS CSF/MNMM. Twenty-four hours later cells were fixed in 4% PFA for ChAT and ApoB immunocytochemistry. 

ALS CSF and ApoB induce human motor neuron degeneration, as indicated by significantly smaller ChAT⁺ clusters compared to the media cultures. In contrast, ALS CSF and ApoB have no effect on the size of ChAT⁺ motor neuron clusters co-cultured with human astrocytes. ApoB staining intensity on ApoB-treated motor neurons is significantly reduced in the co-cultures vs. monocultures.

Healthy astrocytes appear to protect motor neurons from the neurotoxic effects of ApoB by reducing uptake of ApoB into motor neurons. This suggests that intrinsic defects in ALS astrocytes disrupt this neuroprotective function, leaving motor neurons susceptible to ApoB-mediated degeneration. Future experiments will seek to elucidate how astrocyte dysfunction contributes to motor neuron degeneration in ALS.