TRAP-seq of spinal cord motor neurons from ALS diseased mice versus healthy mice

Amyotrophic lateral sclerosis (ALS) is an incurable neurological disease featuring progressive loss of motor neuron (MN) function in the brain and spinal cord. Mutations in TARDBP, encoding the RNA-binding protein TDP-43, are one cause of ALS and TDP-43 mislocalization in MNs is a key pathological feature of >95% of ALS cases. While numerous studies support altered RNA regulation by TDP-43 as a major cause of disease, specific changes within MNs that trigger disease onset remain unclear. Here, we combined Translating Ribosome Affinity Purification (TRAP) with RNA sequencing to identify molecular changes in spinal MNs of TDP-43–driven ALS at motor symptom onset. By comparing the MN translatome of hTDP-43A315T mice to littermate controls and to mice expressing wildtype hTDP-43, we identify hundreds of mRNAs that were selectively up- or downregulated in MNs. We validated effects on Tex26, Syngr4, and Plekhb1 mRNAs in an independent TRAP experiment. Moreover, by quantitative immunostaining of spinal cord MNs we found corresponding protein level changes for SYNGR4 and PLEKHB1. We also observed these changes in spinal MNs of an independent ALS mouse model caused by a different patient mutant allele of TDP-43, suggesting that they may be a general feature of TDP-43-driven ALS. Thus, we have identified two new proteins deregulated in MNs at motor symptom onset in TDP-43-driven ALS models. This spatial and temporal pattern suggests that deregulation of these proteins could be functionally important for driving the transition to the symptomatic phase of disease. mRNA of Chat+ spinal cord motor neurons derived from mice with TDP43^A315T mutation and control mice (wildtype and TDP43^WT) was enriched by translating ribosome affinity purification (TRAP) and sequenced by RNA-seq.