NAD + precursor supplementation modulates neurite complexity and survival in motor neurons from ALS models.

AIMS: Increasing nicotinamide adenine dinucleotide (NAD⁺) availability has been proposed as a therapeutic approach to prevent neurodegeneration in amyotrophic lateral sclerosis (ALS). Accordingly, NAD⁺ precursor supplementation appears to exert neuroprotective effects in ALS patients and mouse models. The mechanisms mediating neuroprotection remain uncertain but could involve changes in multiple cell types. We investigated a potential direct effect of the NAD⁺ precursor nicotinamide mononucleotide (NMN) on the health of cultured iPSC-derived human motor neurons and in motor neurons isolated from two ALS mouse models - i.e., mice overexpressing wild-type TDP-43 or the ALS-linked mutant hSOD1</sup>G93A<sup>.

RESULTS: NMN treatment increased the complexity of neuronal processes in motor neurons isolated from both mouse models and in iPSC-derived human motor neurons. In addition, NMN prevented neuronal death induced by trophic factor deprivation. In mouse and human motor neurons expressing ALS-linked mutant SOD1, NMN induced an increase in glutathione levels, but this effect was not observed in non-transgenic or TDP-43 overexpressing motor neurons. On the other hand, NMN treatment normalized the TDP-43 cytoplasmic mislocalization induced by its overexpression.

INNOVATION: NMN can directly act on motor neurons to increase the growth and complexity of neuronal processes and prevent the death induced by trophic factor deprivation.

CONCLUSION: Our results support a direct beneficial effect of NAD+ precursor supplementation on the maintenance of the neuritic arbor in motor neurons. Importantly, this was observed in motor neurons isolated from two different ALS models, with and without involvement of TDP-43 pathology, supporting its therapeutic potential in sporadic and familial ALS.