ALS sensitive spinal motor neurons enter a degenerative downward spiral of impaired splicing and proteostasis

Despite clear therapeutic potential, the mechanisms that confer differential neuronal sensitivity are not well understood. During Amyotrophic Lateral Sclerosis (ALS), sensitive spinal motor neurons (SpMN) die while a subset of rostral cranial motor neurons (CrMN) survive. In this work, we optimized a protocol to differentiate CrMNs and SpMNs from human induced pluripotent stem cells (iPSCs) by direct programming and positional patterning. Human iCrMNs are more resistant than iSpMNs to proteotoxic stress and rely on the proteasome to maintain proteostasis. iCrMNs better prevent mislocalization of TDP43 from the nucleus, a hallmark of ALS progression. iSpMNs contain more splicing defects than iCrMNs in response to ALS-related stress with genes involved in splicing and proteostasis maintenance. Therefore, iCrMNs resist ALS at two levels, preventing protein accumulation and reducing splicing defects in response to TDP43 nuclear depletion. Thus, ALS-sensitive iSpMNs appear to enter a downward spiral compromising their ability to maintain proteostasis and splicing.