Synaptic TDP43 in the Adult Mouse Brain

Project Summary/Abstract Cognitive impairment due to neurodegeneration plagues 20% of the world population by age 65, yet the mechanistic underpinning of pathogenesis is unknown. A growing number of studies show that the abnormal cytosolic accumulation of TDP43 (transactive response DNA binding protein) is found broadly across neurological disorders, including Alzheimer’s Disease (AD) and Frontotemporal Dementia (FTD). Notably, the severity of accumulation correlates with the extent of cognitive impairment. Given that TDP43 dysfunction also drives synaptic loss, one of the strongest neuropathological correlates of cognitive dysfunction, my long-term goal is to determine the relationship between TDP43 function and cognition using integrative multi-omics as a principal investigator at an R1 institution. To determine how TDP43 dysfunction might underlie cognitive impairment, I am using TurboID-based proximity labelling to identify the TDP43 interactome in adult mouse brain. TDP43-TurboID biotinylates nearby proteins independent of interaction strength. Using this approach, I have identified novel TDP43 protein interactors, including many (~25%) synaptic proteins. By assaying the interactome in synaptosome preparations, I have also found that TDP43 interacts with ribosomal proteins, consistent with its role in synaptic local translation. Importantly, the presence of TDP43Q331K, a causative mutation for ALS and FTD, changes the number of synaptic protein interactions, suggesting that TDP43 function at the synapse may be altered in disease. TDP43-TurboID biotinylates proteins rapidly, and I have used this to reveal that the TDP43 interactome changes upon neuronal activity. Through this, I have identified two key changes that are the basis of the F99 and K00 phase of my application. After neuronal activity, the most robustly increased interactors of TDP43 are glycolytic enzymes. This was notable because glycolytic enzymes concentrate into RNA dependent condensates upon neuronal activity to enhance energy production at the synapse, and TDP43 is a well-known scaffold for RNA dependent condensate formation. Given that glycolytic changes have been associated with plaque formation, synaptic loss, and cognitive impairment, in the F99 phase of this proposal, I will test the hypothesis that upon neuronal activity, TDP43 acts to create condensates of glycolytic enzymes to enhance glycolysis. Additionally, βcatenin and TDP43 interact significantly more following activity. Given that previous work revealed transcription dependent on this interaction, in the K00 phase I will use a multi-omic approach to determine if TDP43 relays information from the synapse to the nucleus to regulate gene expression in the healthy and disease adult brain.