INVESTIGATING TDP-43-MEDIATED TRANSLATIONAL REPRESSION IN MOTOR NEURONS IN A DROSOPHILA MODEL OF AMYOTROPHIC LATERAL SCLEROSIS

Abstract

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive motor neuron loss, resulting in paralysis, muscle atrophy, and ultimately death. TAR DNA-binding protein 43 (TDP-43) is hypothesized to sequester mRNAs into insoluble aggregates within the cytoplasm of motor neurons, thereby translationally repressing a host of mRNAs. In this thesis, a Drosophila model of ALS is used to determine if the mRNA that encodes the glypican dally-like protein (Dlp) is a target of TDP-43 in the disease state. In the context of TDP-43 proteinopathy, Dlp is depleted at the larval neuromuscular junction (NMJ) but accumulates in puncta within the ventral nerve cord (VNC). This suggests that pathological TDP-43 may dysregulate Dlp translation, axonal transport, and intracellular trafficking. To determine the contribution of Dlp to TDP-43-dependent toxicity, I overexpressed dlp and found that it significantly improves Drosophila lifespan and locomotor function in TDP-43WT flies. However, dlp overexpression does not promote survival past the pupation stage in flies expressing TDP43G298S. To validate these findings from Drosophila in humans, I evaluated protein levels for the human Dlp orthologs GPC4 and GPC6 in spinal cord extracts from ALS patients using Western blots. These experiments showed significant variation in GPC4,6 levels depending on the disease mutation and spinal column region. Overall, the results of this investigation together with recently published data from the Zarnescu laboratory suggest an involvement of Dlp in TDP-43-mediated motor neuron degeneration that merits further analysis.