Investigating the role of the RNA binding protein TDP-43 in Amyotrophic Lateral Sclerosis using animal and cell-based models of disease

TDP43 is an RNA and DNA binding protein that has been shown to play an integral role in disease mechanisms that underlie ALS. In fact, a common feature of the vast majority of ALS cases is the presence of TDP-43 aggregates in postmortem tissue from the brain and spinal cord. This finding has spurred research to understand the physiological roles of TDP-43 in the absence of disease, and how these roles are affected by disease. Current TDP-43 mouse models fail to faithfully and reproducibly recapitulate key aspects of ALS, possibly due to the transgenic approaches used. To address these concerns, we generated a targeted, conditional mouse model, and embryonic stem cell lines expressing either human WT or M337V mutant TDP-43 at equivalent levels. We show that expression of mutant hTDP-43 in mice with a mixed genetic background leads to selective motor neuron loss, muscle weakness and premature death. However this disease phenotype is not observed with the same TDP43 mutation in a pure Bl6 background. We next sought to identify alterations in the biochemistry of the mutant protein that may underlie its toxicity, such as its interactions with RNA and protein. By creating a library of RNAs bound by TDP-43 in the mouse spinal cord, we found that the M337V mutation does not compromise the ability of TDP43 to bind to target mRNA transcripts, although the mutation does lead to changes in expression of genes known to be involved in inflammation. In addition, we identified 22 proteins that bind to TDP43 in an RNA-dependent manner, and found that the M337V mutation does not alter these interactions. This work establishes novel mouse and cellular models that provide insights into the functions of normal and ALS-causing mutant TDP43 protein.