Neurodegenerative diseases are an ever-increasing burden within our ageing population, with over 1 in 3 people affected globally, and a lack of effective treatments. Neurodegenerative disorders are broadly characterised by the gradual deterioration and death of neurons in the brain and/or spinal cord causing irreversible damage to the nervous system, leading to a decline in cognitive function and/or motor skills amongst other neurological functions. Genetic, environmental factors and general ageing are all risk factors for neurodegeneration, driving complex pathological mechanisms that underly disease development and progression. Dissecting these disease mechanisms therefore becomes a critical issue, as a better understanding of fundamental mechanisms will allow more development of effective therapeutic interventions.
This thesis investigates a critical protein, TAR DNA-binding protein 43 (TDP-43), an RNA-binding protein which is closely linked to many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In 2019, an ALS and FTD-associated RNA-binding deficient mutation of TDP-43 was identified, K181E. To study how RNA-binding deficiency contributes to TDP-43-mediated neurodegeneration in disease-specific contexts, the mutation was introduced to three separate models alongside wild-type TDP-43 and C-terminal mutations: at endogenous levels in a human neuroblastoma cell line, via overexpression in primary rodent cortical and hippocampal cells, and through overexpression in Drosophila melanogaster. Using these models, we characterised the localisation and functional effects of K181E-TDP-43 in neurons and astrocytes, identifying a novel neuronal overgrowth phenotype in K181E-TDP-43-neurons in response to activation of the stress-responsive JNK/AP-1 signalling pathway, potentially underlying its involvement in both cognitive and motor dysfunction. Furthermore, we observe TDP-43-mediated dysfunction in neuron-astrocyte interactions, irrespective of RNA-binding capability, contributing to non-cell autonomous mechanisms of toxicity. Overall, by using these models, this study unveils how disease-associated RNA-binding deficits contributes to TDP-43 proteinopathy in ALS/FTD, providing a deeper understanding of these overlapping disorders and neurodegenerative diseases as a whole.
