Toward better models of neurodegeneration: RNA binding-deficient acetylation-mimic TDP-43 drives neuronal dysfunction and pathology in in vitro and in vivo model systems

Transactive Response DNA-binding protein 43 kDa (TDP-43) is a nucleic acid binding protein known for its function as a master regulator of RNA processing, and for its dysfunction in disease. TDP-43 proteinopathies are a group of neurodegenerative disorders in which TDP-43 becomes dysfunctional, mislocalized, and aggregated within neurons and glia. The major TDP-43 proteinopathies are amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), both of which are incurable, age-related disorders that usually arise sporadically. It is not understood how TDP-43 becomes dysfunctional in sporadic illness, however post-translational modifications (PTMs) of the TDP-43 protein may play a role. A better understanding of the pathogenesis of TDP-43 proteinopathies is needed, however this is difficult to achieve without reliable disease models. Herein, I describe novel models of TDP-43 proteinopathy based on the premise that TDP-43 acetylation, or an acetylation-mimic mutation at lysine 145 (K145), triggers a pathogenic cascade of reduced RNA binding capacity, TDP-43 mislocalization from the nucleus to the cytoplasm, and increased aggregation propensity. In chapter 1, I lay the groundwork for this dissertation by discussing TDP-43 biology and what is known about TDP-43 dysfunction in neurodegeneration. In chapter 2, I show that expression of endogenously encoded acetylation-mimic TDP-43K145Q in mouse primary cortical neurons and human induced pluripotent stem cell (hiPSC)-derived cortical neurons leads to stress-induced nuclear foci formation, altered TDP-43 subcellular distribution, and impaired splicing. In chapter 3, I describe a novel mouse model of TDP-43 proteinopathy in which the endogenous mouse Tardbp gene was modified to express aberrant RNA binding deficient acetylation-mimic TDP-43K145Q. These mice develop FTLD-like age-dependent cognitive impairment, TDP-43 mislocalization and aggregation, and prominent transcriptomic and splicing abnormalities. In chapter 4, I identify potential disease-modifying genes and evaluate their ability to reduce pathologic TDP-43 species in a cellular model of TDP-43 proteinopathy. In chapter 5, I summarize my key findings and discuss outstanding questions and future directions inspired by this work. In summary, this dissertation investigates the role of TDP-43 acetylation in TDP-43 dysfunction and describes new models of TDP-43 proteinopathy that can be utilized to interrogate disease mechanisms and design targeted therapeutics to combat neurodegeneration.Doctor of Philosoph