Hamilton, Joseph;
(2022)
Functional analysis of FAN1 and DNA
repair expression in somatic expansion
of the HTT CAG repeat.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Huntington’s disease is a monogenic neurodegenerative disorder caused by a CAG trinucleotide repeat expansion at the HTT locus (≥36 repeats) and clinically characterised by a triad of progressive cognitive, psychiatric and motor phenotypes. Age at motor symptom onset is primarily dictated by the length of the HTT CAG repeat tract, which exhibits pathogenic expansion in somatic tissues throughout a gene carrier’s lifetime. Recent genome-wide association studies converged on DNA repair loci as significant modifiers of residual age at onset variation. These genes constituted elements of the mismatch repair pathway (i.e., MSH3, MLH1, and PMS2), in addition to the interstrand crosslink repair nuclease FAN1, which are collectively known to moderate somatic expansion. Despite this insight, the protective mechanism of FAN1 remained unestablished and it was unclear if DNA repair protein expression dictated the regional nature of expansion observed in the Huntington’s disease brain. Therefore, structure-function studies were performed with GFP-FAN1 variants in FAN1 -/- U2OS cells expressing an exogenous HTT 118Q exon 1 construct. These experiments identified a dual mechanism whereby FAN1 attenuates somatic expansion via inherent nuclease activity and sequestration of MLH1 from the mismatch repair network. Although limited by expression levels, generation of HD 125Q FAN1 -/- and nuclease-inactivated FAN1D960A/D960A induced pluripotent stem cells mainly corroborated these findings. Finally, inter-tissue quantification in HD R6/2 and zQ175 mouse models suggested that varying expression levels of DNA repair proteins is not the primary determinant of somatic expansion propensity in mice. These data provide mechanistic insight into Huntington’s disease pathogenesis and highlight the FAN1-MLH1 interaction as a novel therapeutic target.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Functional analysis of FAN1 and DNA repair expression in somatic expansion of the HTT CAG repeat |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/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. |
| Keywords: | FAN1, DNA repair, Huntington's disease |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Neurodegenerative Diseases |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10162238 |
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