Title

Cell-Based Models and RNA Biology for a Genetic Form of Lou Gehrig's Disease

Date of Award

5-1-2020

Degree Name

Doctor of Philosophy

Department

Molecular Biology, Microbiology and Biochemistry

First Advisor

Gagnon, Keith

Abstract

Microsatellites, or simple tandem repeat sequences, occur naturally in the human genome and have important roles in genome evolution and function. However, the expansion of microsatellites is associated with over two dozen neurological diseases. A common denominator among the majority of these disorders is the expression of expanded tandem repeat-containing RNA, referred to as xtrRNA, which can mediate molecular disease pathology in multiple ways. Frontotemporal Dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS) are two fatal neurodegenerative diseases with significant clinical, neurological and genetic overlap thus referred to as C9FTD/ALS. Currently, gaps in the study of the underlying disease mechanisms persist, which can aid in the identification of promising therapeutic approaches. Access to simple models of neurological repeat expansion disease is critical for investigating biochemical mechanisms and for early therapeutic discovery. To better understand the molecular pathology of C9FTD/ALS repeat expansion disorder, we cloned GGGGCC repeats, which are the leading genetic cause of C9FTD/ALS. We employed a recursive directional ligation (RDL) technique to build multiple GGGGCC repeat-containing vectors and validated the cloning to facilitate step-by-step characterization of disease mechanisms at the cellular and molecular level using these vectors. In this study, we also differentiated C9FTD/ALS patient-derived induced pluripotent stem cells (iPSCs) to neural stem cells (NSCs) to be used as model systems. The use of iPSCs and NSCs to reveal important insights into the pathogenic mechanisms and to generate multiple neural cell types presents an excellent opportunity for researchers to model neurodegenerative diseases for cell therapy and drug discovery. We further investigated potential nuclear export mechanisms for C9FTD/ALS xtrRNA. The nuclear export mechanisms of xtrRNA in C9FTD/ALS are not well studied. ASOs and siRNAs were employed to knockdown genes of interest to study their involvement in the nuclear export of xtrRNA. We saw promising results on knockdown of TorsinA involved in nuclear export of xtrRNAs, corroborated by a substantial increase in the average number of xtrRNA foci in the nucleus. Our initial study provides evidence that TOR1A may be involved in the nuclear export of aberrant C9FTD/ALS repeat-containing RNAs. Due to the lack of reliable and robust assays to detect RAN translation products, the effect of the knockdown of TorsinA in these cell lines still remains to be explored. But the current study lays the groundwork for a deeper understanding of the less-studied nuclear export mechanisms in C9FTD/ALS and could reveal new therapeutic approaches to selectively block the nuclear export of xtrRNA through the use of RNAi and ASOs. The insights gained from this study will help us understand future events in the xtrRNA life cycle such as repeat translation mechanisms.

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