Giblin, Ashling;
(2024)
Investigation of genetic modifiers of C9orf72 toxicity in Drosophila and iPSC neuron models.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
A GGGGCC repeat expansion mutation in the C9orf72 gene is the most common genetic cause of both ALS and FTD. However, the key downstream effector pathways mediating neuronal loss are still unclear. The aims of this thesis were to reveal novel insights into the pathogenesis of C9orf72 ALS/FTD using (G₄C₂)₃₆ Drosophila models, to identify protective genes and pathways for further investigation. First, I investigated the protective effects of odd and bowl, previously identified in a genetic overexpression screen for suppressors of (G₄C₂)₃₆ toxicity. Novel transgenic Drosophila expressing the human orthologs of odd and bowl, OSR1 and OSR2, extended C9 fly survival when overexpressed in adult neurons. The extent of survival benefit varied between the genes tested; odd and OSR2 produced greater survival extensions than bowl or OSR1, attributable to odd and OSR2 decreasing DPR levels. Next, I characterised Trpγ, as a modifier of C9 toxicity. Trpγ was upregulated at an early timepoint in C9 flies. Furthermore, Trpγ orthologs TRPC4 and TRPC5, were upregulated in patient-derived iPS motor neurons, while TRPC4 was downregulated in C9ALS post-mortem cortical neurons. Overexpression of Trpγ improved multiple neurodegenerative phenotypes in C9 flies, in part by reducing levels of toxic poly(GR), suggesting that early upregulation of Trpγ is a protective response. Lastly, I performed RNA sequencing on C9 fly heads at an early timepoint to identify early dysregulated pathways and found downregulation of fatty acid synthesis and desaturation pathway genes. Remarkably, this signature was conserved in a transcriptomic dataset of human ALS spinal cord. Lipidomic analyses of C9ALS/FTD iPSC-neurons and FTD post-mortem brains revealed a striking loss of highly unsaturated phospholipids. Desaturase overexpression was sufficient to extend survival in C9 flies and protect against excitotoxicity in C9 iPSC-derived motor neurons, implicating altered neuronal phospholipid saturation as a novel pathway in C9ALS/FTD pathogenesis.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Investigation of genetic modifiers of C9orf72 toxicity in Drosophila and iPSC neuron models |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2024. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) Licence (https://creativecommons.org/licenses/by-nc-nd/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10185976 |
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