The mislocalization and aggregation of RNA-binding proteins (RBP) is a pathological hallmark of Amyotrophic Lateral Sclerosis (ALS). The RBP TAR DNA-binding protein 43 (TDP-43) is of particular interest, as pathological aggregation of TDP-43 is observed in nearly 97% of ALS patients, despite the fact that disease-causing mutations in TDP-43 explain fewer than 5% of disease incidence. This observation suggests that misregulation or mutation of other genes converge on TDP-43 pathology, however it remains poorly understood how the aggregates arise or whether they can be reversed or prevented. To this end, we have developed Pulse-Shape Analysis-based aggregation reporters for the TDP-43 that, when coupled to fluorescence activated cell sorting, quantifies aggregation at the single cell level. This reporter was leveraged against a genome-wide CRISPR- Cas9 knockout screen to identify regulators of TDP-43 aggregation. Reassuringly, this screen revealed known interactors and pathways involved in TDP-43 regulation and pathology. Additionally, this work revealed several novel proteins not previously implicated in TDP-43 biology or aggregation. Initial follow up on one top hit, SRRD, revealed that this protein reduces TDP-43 aggregation in a mammalian aggregation model, and reduces TDP- 43-associated toxicity in a yeast model, indicating that these genes indeed modify TDP-43 aggregation. The goal of this proposal is to mechanistically dissect how these novel regulators modify TDP-43 aggregation. Using an induced motor neuron model of TDP-43 aggregation, yeast toxicity models, and in vitro studies, I will assess the interactors, signaling pathways, and mode of TDP-43 modification for the following four genes: METTL5, EIF2AK2, XPO4, and SRRD. This work will not only reveal the function of uncharacterized proteins, but dissect their heretofore unknown mechanisms in regulating TDP-43 aggregation. Through better understanding of how TDP-43 aggregation is regulated, the field can begin to answer questions regarding the role of TDP-43 aggregation in disease pathogenesis and progression. By understanding the regulatory network of underlying TDP-43 aggregation, we can begin to therapeutically modulate the pathways that contribute to disease.

Public Health Relevance

Aggregation of the RNA-binding protein TAR DNA-binding Protein-43 (TDP-43) is a pathological hallmark of Amyotrophic Lateral Sclerosis, a devastating neurodegenerative disease, however, it is poorly understood how aggregates arise, or whether they can be reversed or prevented. Using a genome-wide CRISPR-Cas9 knockout screen, I identified several novel regulators of TDP-43 aggregation. A mechanistic understanding of how these modifiers regulate TDP-43 aggregation will provide a fresh perspective on this heavily studied topic, and will inform the development of more effective therapeutics for Amyotrophic Lateral Sclerosis.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1)
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Gubitz, Amelie
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University of Pennsylvania
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